In 1937, the Peel Commission suggested a partition of what was then British Mandatory Palestine into two states: one for the Jews, and one for the Arabs. It was accepted by the Jews, but not by the Arabs who refused to accept the existence of even a small Jewish state. 

In 1947, partition into two states was again proposed by the UN Special Committee on Palestine. Resolution 181 was passed by the UN General Assembly, which authorized the establishment of a Jewish state. Israel was established, but the Palestinian state was not, again, because they refused to accept a Jewish state as its neighbour in the Middle East. 

In the 1990s, the Oslo Accords led to the recognition of the PLO as the representative body of the Palestinians. The Oslo Accords led to the Road Map for Peace which led to the Annapolis Conference, which has led to Israeli Prime Ministers endorsing a two-state solution that would see a Palestinian state created alongside Israel. It is the only way for a Jewish, democratic state to exist alongside a Palestinian state. 

A call for a one-state solution is a call for the dissolution of the Jewish State of Israel and replacing it with a majority-Arab state in which Jews would no longer be able to exercise self-determination. A two-state solution is thus the only viable solution for a peaceful future to the Israeli-Palestinian conflict.