At various times in its history, the United States has gone through oscillating periods of isolationism and then greater international involvement. Many other nations have also taken strong stances on one side of this issue or the other. Let's at some of the merits of each stance.
Those who argue for isolationism and non-involvement could claim that it provides more domestic peace. This is particularly the case in multi-ethnic countries like the United States. Woodrow Wilson attempted to keep the country out of World War I by arguing that he did not want to divide the loyalties of a country that had many citizens of both English and German descent.
Isolationism also allows a country to focus on its own domestic economy. While war provides many opportunities for increased production and work programs, it remains bad for trade overall. While other countries are at war, a non-interventionist country can take advantage of new market opportunities and fill in supply and market gaps left by warring countries.
Non-intervention is also a way to protect a nation's safety during certain conflicts. Switzerland, for instance, has long been surrounded by other countries frequently at war with each other. By refusing to pick sides, Switzerland has avoided being dragged into a conflict that is not of its making; neither has it created powerful enemies of certain neighbors.
More bellicose and interventionist voices often point out the folly of the above arguments. Non-intervention leaves open the opportunity for bad actors to cause harm that reverberates at home. Today, many maintain that if the United States were to take a completely non-interventionist role in the Middle East, other rivals, such as Iran and Russia, would fill the power vacuum. Their influence could lead to bigger problems for the US down the road.
Many view the US military, as well as those of certain other countries, to be peacekeeping forces when all things are considered. A weakness of isolationism is that it can allow matters to worsen up the point where a large-scale, dangerous intervention becomes necessary and inevitable. This was the case when the US and UN failed to intervene in Bosnia in the early 1990s. Eventually, the situation devolved to the point where a large multi-national force needed to intervene and quell the ballooning conflict. A similar argument has been made the United States could have helped end both world wars more quickly if it joined war efforts earlier. In both conflicts the US waited until its hand was forced to support their side directly.