A summit including both Western and Eastern states of Europe was launched in Helsinki, with the Helsinki Final Act being signed in 1975.  This treaty recognized all national borders in Europe and outlawed the use of force to change these borders. The Act stated that “the participating states regard as inviolable all one another’s frontiers as well as the frontiers of all states in Europe and therefore they will refrain now and in the future from assaulting these frontiers. Accordingly, they will also refrain from any demand for, or act of, seizure and usurpation of part or all of the territory of any participating state”. As also understood from the information given the correct answer is A.

The information about the treaties taking place in the other options are as follows:

The de-escalation of the Cold War in Europe also affected the relationship between the bloc leaders. The United States and the Union of Soviet Socialist Republics began negotiations to decrease their nuclear arsenals. The Strategic Arms Limitation Talks bore fruit when the first Strategic Arms Limitations Treaty was signed in 1972. In 1979 both parties found common ground to sign a section treaty, although the United States withdrew from the treaty in 1980, thus blocking any further cooperation between the two superpowers

A third bloc of states appeared in the mid-1950s that wanted to distance itself both ideological camps. This was the so-called Non-Aligned Movement, a collective movement of states that had only recently gained their independence from Western imperial powers.

The United States organized The Hague Conference of 1907 to determine a set of common values and diplomatic practices. One significant decision taken at that conference called for the creation of a permanent international organization within seven years, one where states would be equally represented and where they could resolve their disputes through negotiations.

In January 1919, the Paris Peace Conference convened to negotiate peace agreements that would shape the new international system.