Who would you talk to, to help with foreign problems?

So a situation like famine in another country, how would you address this problem to here in the u.s.? I was thinking about a solution like protesting/lobbying but to whom though? would it even work? Senators only deal with stuff in the u.s. right? Which part of the government deals with foreign problems/situations like the nuclear weapons in other countries, if possible famine in other countries?