The answer to this really depends on which century you are talking about. The US has been drawn deeper into international politics in the early years of all three centuries of its existence. I am going to assume that you are talking about the 19th century.
In the early years of the 1800s, the Napoleonic Wars in Europe got the US more deeply involved in international politics. As France and England fought each other, their conflict spilled over to the US. This happened mainly because each side started to try to confiscate US shipping headed to the other country. This caused the US to almost go to war with France and then, eventually, to go to war with Great Britain in 1812.
The Napoleonic Wars, then, pulled the US into international politics because those wars caused issues between the US, England, and France over freedom of the seas.