What central issues drew the United States deeper into international politics in the early years of the century?(1914-1920)
The short answer here is the World War I drew the United States deeper into international politics. The US had thought it could remain aloof, but as the war continued, issues relating to the war forced the US to get more involved. After the US got into the war, Woodrow Wilson's desire to fix the world led to further US involvement in international politics.
The main issue that got the US involved in the war was the idea of freedom of the seas. The US wanted to trade with Great Britain but was stopped from doing this by a German submarine blockade. This forced the US to get more involved in the war.
As the war was ending, Wilson wanted to make later wars less likely through his 14 Points. This also made the US get more involved in international affairs.
World War I and the postwar Europe that followed was the central issue, but there were others as well. The Russian Revolution began in 1917, the first communist revolt in the world. A civil war between communists and those loyal to the Czar began, with the US and some of our allies backing the non-communists with foreign aid.
Back home, the First Red Scare took place in 1919 as fear of a communist revolt in America was a result of the events in Russia.
President Woodrow Wilson's involvement in peace efforts at Versailles after World War I led to the creation of three new countries: Poland, Czechoslovakia, and Yugoslavia. At that point, we were one of the few empires left standing after the war, and our place on the world stage reflected that.
The primary issues that drew the United States into the First World War was concern over what was happening in Europe. With growing and emergent challenges in the region, the interaction of the United States was almost inevitable. The growth of nationalism and imperialism both within Europe and outside of it, the dwindling of resources and economic opportunities, and the challenges posed to democratic nations helped to pull the United States into the conflict. On the other side, some argue that the threat that the Central Powers posed to the economic interests of America also played a role in the entry into world conflict.