I assure you that the US, like other "great powers" don't help other countries by altruism.
For example, a third world country may have cheap labor, natural resources, a heavily polluting industry, etc... that can be exploited by the US. But a country that is starving or at war isn't productive, so the US sends "help". The worst part is that the third world country may actually do very well by itself but the more resources the country spends sustaining itself, the less are available for the US to exploit.
There may be other reasons, such as using other countries as buffers to keep conflicts out of our own territory.