The International System is one of the core concepts in the field of International Relations. A “system” is either a whole or a network consisting of multiple units that interact within the framework of defined rules.

We can elaborate on this general definition to specify the core features of the international system. According to K. J. Holsti, the international system is “any collection of independent political entities -- tribes, city states, nations or empires -- that interact with considerable frequency and according to regularized processes” (Holsti, 1995:23).

According to Bull, an international system has three defining characteristics:
1. First, it requires the presence of multiple sovereign states.
2. Second, regular relations and interactions of these states must exist as a part of a system.
3. Third, these states must act while being bound by shared rules and norms that bring them together. (Bull, 1995: 225)

From this assessment, we can conclude that the Peace of Westphalia in 1648 constituted the starting point of the international system: Europe adopted a specific kind of sovereignty and regular interactions among mutually-recognized sovereign states emerged.

It was the Protestant uprising of Bohemia in 1618 against the repressive rule of the Habsburg dynasty. The Bohemian revolt became stronger; it gained the support of the Evangelical Union. However, the revolt was suppressed by the Habsburgs following a two-year long military campaign. Staring in 1620 and supported by the Pope, Habsburg Emperor Ferdinand II began to invade the member states of the Evangelical Union. The conflict escalated as the northern Protestant states of Denmark and Sweden joined in. After the French, too, entered in 1635, on the side of the Protestants, all the states in continental Europe joined the war. Thus, the war took its final shape, one in which, apart from numerous middle and small participating states, France and Sweden confronted the Spanish and Austrian Habsburgs.

Possibly it was, considering the original motive of some of the participants. Nevertheless, the gains and losses of both sides led to a new status quo. The later stages of the war forced rulers to pursue policies based on their own political interests.
A prominent European historian, Stephen J. Lee, argues that “throughout the war strategic interests were of paramount importance and religion could be seen as a convenient form of justification for devious diplomacy and as a veil for cynical political decisions” (Lee, 1984: 83).

Thus, it was that the Westphalian settlement launched an international system of independent and territorially-conceived sovereign states, a system that acted based on common rules and established regular patterns of relationships. First and foremost, the Westphalia system paved the way for the formation of a structure that enabled all political actors within the scope of the system to participate in the conduct of the system itself. The primary actor of the Westphalian system became not the Catholic Church but the sovereign and legally equal state (Stirk, 2012, 644).

Hegemony refers to a situation in which a powerful state or a coalition of powerful states shapes the international system through a set of coercive and non-coercive instruments. The United Kingdom in the nineteenth century and the United States since 1945 are prime examples of hegemonic powers (Kwon, 2011: 594-595).

The most remarkable characteristics of the international system that emerged after the year 1648 were:
• its limited geography,
• similar political units, and
• a developing pattern of relationships basedon the dynamics of conflict and cooperation between these units.

The Westphalian system at its earlier stages was a geographically narrow central European system. At that time, Europe was composed of monarchies that mutually recognized their borders and sovereignty within their domains. For that reason, the boundaries of the international system only covered political units that acknowledged the sovereign equality of each other.

Between 1648 and 1789, each succession war was concluded with a peace settlement following an international diplomatic congress that included all the warring parties, as noted in Table 2.1. The Peace of Utrecht put an end to the Spanish Succession Wars in 1713, for instance.

At these congresses, inter dynastic kinship also facilitated compromise rather than punishment. Congress diplomacy rarely had a transformative impact on the structure of the international system. Instead, it served to restore the status quo and confirm the international system established by the Peace of Westphalia.

Both winners and losers of wars had a role to play in the construction of peace. In this period, the principle of sovereign equality provided both powerful and small states with the opportunity of equal representation within the framework of congress diplomacy. The international system based on the principles of the Peace of Westphalia prevailed and was consolidated.

One significant innovation of the French Republic was the formation of the citizen-army. It enabled France to conscript large numbers of citizens to fight Revolutionary Wars. This mass conscription not only brought military success to the Republic but also led to a shift in the military tactics of other European powers. Wars that had been fought previously by mercenaries, paid employees of the monarchies, were now fought by large numbers of citizen-soldiers.

Even though every European state appeared at the Congress of Vienna, final decisions ultimately were made by the four major powers: Austria, Britain, Prussia, and Russia. They focused particularly on territorial rearrangements in Europe. To ease their security concerns, they abolished new political units created by Napoleon.
They also wanted to prevent any future revolution in Europe inspired by the French revolution. Therefore, ancient régimes (former monarchical regimes) were restored in France, Spain, and the Netherlands. As such the Congress of Vienna marked a return to a Europe composed of monarchies (Kissinger, 1957: 176).

The struggle between conservative monarchies and revolutionary movements had a profound impact on the nature of European politics in the 19th century. After 1815, European states were not only restored as monarchies but were also
committed to collectively preserve the monarchical nature of the international system.

To that end, they constructed a two dimensional collective security mechanism:

First, members of the Concert cooperated against internal threats from liberal or nationalist movements. The great powers, therefore, assumed the right to intervene in states threatened by internal revolutionary upheavals. As a result, the great powers suppressed revolutionary uprisings in Italy and Spain.

Second, the great powers kept France in check, since it was still considered a potential center for (and source of) revolutionary movements.

The Congress of Paris demonstrated the failure of the Concert of Europe, which had turned into a zero-sum game. The settlement imposed by Britain undermin-ed not only Russia’s power but also the Quadruple (and later the Quintuple) Alliance’s position. This heralded the end of the great power hierarchy that had maintained the status quo and a certain pattern of cooperation since 1815.

Bismarck’s foreign policy priority was the security of Germany.
• He created a system of alliances under his control. This system aimed to:

• neutralize the rivalry between Germany’s neighbors, as well as to isolate France from the European system, and
• reinforce common values that would facilitate great power cooperation in the
post-1815 era (Taylor, 1971: 255-278).

• In 1872, Bismarck devised the Three Emperor’s League between Austria-Hungary, Germany, and Russia. A renewed version of the Holy Alliance, this was a semi-official alliance that sought to control Austrian-Russian competition in the
Balkans.

In 1879, Austria-Hungary and Germany also signed an official pact which creat-ed The Dual Alliance between the two countries that lasted until the end of World War I.

• These various agreements formed an overlapping — and often contradictory — diplomatic network. Thus, they included a significant number of secret clauses.

The outcome of World War I signaled the complete collapse of the old European system. By the end of the war, it was evident that the old system had lost its main organizing mechanisms. In November of 1918, Europe was in ruins and the war seemed to have continued forever. Diplomacy had vanished
during the war, and the only solution left to the combatants was to fight it out to the end.

Such a situation generated two primary outcomes. First, European diplomatic values and mechanisms had not only become outdated but also had proved inadequate to prevent major wars on the European continent. Second, this heralded the end of the hegemonic position of Europe in world affairs. It was
not surprising that the attempt to end the war came from a non-European power – the United States. On January 18, 1918, the American President, Woodrow
Wilson, outlined his principles in a speech on war aims to the US Congress that came to be known as the “Fourteen Points.” These principles would constitute the basis for a future peace. They also aimed at the restoration and renovation of the pre-war international system.

In January 1919, the Paris Peace Conference convened to negotiate peace agreements that would shape the new international system. The several outcomes of the Paris Conference were as follows:

• The peace treaties, mainly the Treaty of Versailles, constituted a new Europe in which Germany and other defeated states had substantially lost their pre-war status. This ended the great power model of the Concert of Europe and formed a new great power hierarchy in which Britain and Franceseemed to dominate.

• The conference marked the emergence of great non-European powers (namely the United States and Japan) and the end of European dominance over the international system. It also undermined the value system on which the pre-war international system had been built. The 1907 Hague Conference and Wilson’s Fourteen Points set the basis for the reconstruction of a new set of values for
the emerging international system.

• As the globalization of theinternational system had already been underway before the outbreak of the war, the proposed system structure was made concrete at the Paris Peace Conference by creation of the League of Nations. The League of Nations was designed to serve as a forum where member states could work on a new model of open diplomacy toward solving their disputes.

Serious problems in the international system emerged, overwhelming the League’s efforts.

First, the war reparations brought the German economy to the verge of collapse. Second, revolutionary upheavals broke out in virtually every defeated European state.
Third, to end the turmoil in the defeated states, the United States and Britain proposed a plan that would guarantee recovery of the German economy and the normalization of German foreign policy.

World War II had been a major victory over fascism in which the two biggest aggressors, Germany and Japan, were soundly defeated.

Most of mankind wondered how the new international organization, the United Nations, would work out. Although the new organization was like the League of Nations, it differed in some important respects. Although it was designed to
incorporate all sovereign states in the international system, this proved to be legal equality in the General Assembly rather than political equality, because the five victorious allies (the United States, the Union of Soviet Socialist Republics, Britain, France, and the Republic of China) were given veto power in the Security Council. 

The first post-war ideological confrontation occurred in Europe. As the Soviet Union strengthened its presence through building satellite states in Eastern Europe, America adopted the policy of containment of the Soviet Union. First was the Truman Doctrine in 1947, designed to stop and reverse the expansion
of the Soviet Union, and then a year later the Marshall Plan, a financial aid program for Western European states whose infrastructure had been devastated in the war. The Marshal Plan aimed to restore a democratic Western Europe. Another initiative was launched in 1949 with the establishment of the North Atlantic Treaty Organization. It aimed to foster collaboration on security and defense issues among Western nations.

There were many international relations facets to the Cold War.

• The Cold War was a bipolar system that rested on confrontation between two blocs. It was ideologically defined and led by superpowers who possessed extensive nuclear capabilities.
• The leaders on both sides were determined to keep their blocs under control. The policies and common interests were generally designed by the bloc leader. The leaders provided the members of the bloc with few opportunities to follow their own national interests. Moreover, both the North Atlantic Treaty Organiza-tion and the Warsaw Pact were hierarchical organizations in which the leaders maintained clear dominance over the members.

• Given their security concerns, the balance of terror pushed the minor members of the blocs into bandwagoning with the bloc leader.

• The United Nations still existed as the primary forum for bloc leaders to cooperate against threats emanating from outside of their spheres of influence or against problems with states outside their bloc.

The end of the Cold War heralded the beginning of a new system, a new world order. The bipolar nature of the international system was no more. However, an international crisis erupted in the Middle East when Iraq invaded Kuwait. The United States intervened in this conflict, transforming the nature of the new system. An international consensus called for action by the UN to protect Kuwait, a member state, and a multi-national intervention force, made up of troops from many states from around the world, participated in the fight. This multi-national force effectively forced Iraq out of the invaded territories and restored Kuwait’s sovereignty. The United States had proved to be an effective leader, and nearly every other state viewed American as the sole international superpower.

This new role for the United States gave the system a unipolar character. As the former leader of the liberal bloc, the United States had the opportunity to bring a liberal peace to the system, and there was great hope that with the aid of its powerful military, the Americans would organize the international community
of states to solve the problems that had erupted at the end of the Cold War (Falk, 2004: 25-79).

The rest of the decade, however, did not unfold as expected. Civil wars broke out in Somalia, Bosnia, and Rwanda, and by the end of the 1990s the prestige of the United States had rapidly declined. The consent given to the American leader-ship had been seriously undermined. On the other hand, both the new Russian
Federation and China were on fast tracks, consolidating their power-base and eager to widen their sphere of influence. Although the United States still dominated the international system in economic, political, and military terms, the new rising powers meant that new confrontations were likely to occur.