Mercantilism's system believed that it should limit its imports and that is should depend on its own resources. The huge problem with this is that often times nations don't have the goods that they need, and there were heavy tariffs on foreign goods so it costed them a lot more to buy things. This lead to imperialism, though, because it forced nations to try to expand and control more land to acquire the goods they want without having to spend as much money.
War also increased with the system of mercantilism. This is because, as previously mentioned, nations wanted to expand to get the goods they wanted without having to spend as much money, but this usually turned out to be a bad thing for countries that are already having economic trouble because war is very costly. There isn't ever a guarantee that they'll win, and since that's the only way they'd make money from it, it's an enormous problem for the nation if they lose, especially since losing make it harder for them to influence the people of the country and other countries too.
Mercantilism didn't provide a steady source of income for countries that adapted it. An example of this would what happened between the American colonists and England during the time of the Boston Tea Party. The colonists were being forced to pay ridiculous amounts of money for sugar and tea that their economy couldn't handle at the time, and this led them to revolt and throw all the shipped tea and sugar into the harbor. This was bad for England especially because they lost a lot of money that they had been receiving from the Americans beforehand, dually proving that wars/fighting with countries that adapt mercantilism