this isn't exclusively what foreign aid is spent on, in fact only a small amount is spent on true humanitarian aid depending on what one includes. At the least:
"United States foreign aid is aid given by the United States government to other governments. It can be divided into two broad categories: military aid and economic assistance."
"In the 21st century, the US government operates five major categories of foreign assistance: bilateral development aid (the largest amount), economic assistance supporting U.S. political and security goals, humanitarian aid, multilateral economic contributions, and military aid"
https://en.wikipedia.org/wiki/United_States_foreign_aid
now true humanitarian aid is children starving in Africa for instance. Economic assistance supporting U.S. and political goals may not always support what would be in the best interest of that country, at least it's sometimes criticized for this. Look at the lead countries on receiving foreign aid as well on that same Wikipedia page, more to the middle east (and even quite wealthy countries) than ever gets to Africa (black people not so much so - I suppose we imagine that our foreign aid goes to black people in the same way we imagine blacks are the only ones getting welfare - reality not so much so).