In modern times, Internationalism most commonly means an appreciation for the diverse cultures in the world, and a desire for world peace. Proponents of Internationalism believe in the interconnectedness of mankind, that man is not only a citizen of his country but of the world. Because of this view, Internationalists desire to help the world through leadership and charity. This leadership and charity can take the form of international organizations such as The World Health Organization, The United Nations, and the European Union, which was formed in order to consolidate economies and help all European nations succeed by cooperating together.
In American history, the United States started out being anti-Internationalist. In the Monroe Doctrine, for example, the Americans basically told the world, "You stay out of our affairs and we will stay out of yours." This worked for awhile. Today, however, the world is shrinking. Countries are so intertwined with other countries due to economies, trade, alliances, etc., that it is really, really hard to maintain neutrality. Very few countries have succeeded - Switzerland, being one of the few. That is why countries put their money in Swiss banks in time of war...........but I digress.
Case studies of where Internationalism has been unsuccessful - this would be a matter of opinion, but some people believe The United Nations has been totally ineffective. They are always issuing decrees and imposing sanctions that have no effect on stopping countries like North Korea for doing whatever they want and sticking their tongues out at the United Nations.
Right now, for example, my son is on a Navy ship monitoring the situation in the South China Sea because in spite of warnings by the United Nations FOR YEARS AND YEARS, the North Koreans recently blew up a South Korean submarine, then lied about it and said they did not do it, and if South Korea takes any retaliatory action, it will mean war. The United Nations is having a conference about this, while the U.S. Navy is actually doing something. I know, I'm biased.
If you do some research, you can find other examples of what similar International organizations have accomplished and then make up your own mind.