The United States should be responsible for helping third world countries, as should other first world countries. The US has so many resources that it is possible for the country to help these countries and themselves at the same time. It would allow the US to develop more trading partners, and friends abroad.
I do think the United States is responsible for helping third world countries. We do send quite a bit of aid to these impoverished nations, but it isn't nearly enough. The same rings true domestically. It's time to cut the military budget and start helping the people who need it most.
The United States is not responsible for helping third world countries. All countries need to learn to take care of themselves. America for too long has ben known as a rescuer of foreign countries across the world. It is time to turn off the gravy train and start expecting other nations to help themselves.
The US usually does go and help the third world countries that are in need, but it is not our problem. We need to start trying to fix things here in our country, before we go and try to make sure that everyone else is getting to live like we do.
Every country is ultimately responsible for themselves -- that is a primary condition of sovereignty. Therefore it cannot be said that the United States has a responsibility to take care of any foreign country. However, it may be in the US's interest to help the third world in order to stabilize those countries and promote security and trade. Furthermore, while the US government does not have a responsibility to the third world, that doesn't stop private American citizens from feeling they do on moral grounds, and contributing personally.