Why did americans become more interested in foreign affairs in the late 1800's?

because America was beginning to assert itself as a global power (mainly due to investment in battleships). The first major incident during that time was The USS Maine exploding in Cuba, which lead to the spanish-american war (in part due to yellow journalism that stoked public fear). Spain was "officially" no longer an empire after that conflict, and the US gained territories in Cuba, Guam, the Philippines, and Puerto Rico. This resulted in America now being recognized as a rising global superpower, at a time when the European empires were fizzling out.