First off we have nationalism, which basically was countries saying we are the best, nothing can happen to us because we are just so great. Then we have imperialism. So here we have countries who are fresh and want as much territory as possible and this doesn't really sit well with other nations. Then, this concept called the alliance system pops up which basically drags all these other nations into a war that they really didn't need to be in. The trigger for all this was the assassination of archduke Franz Ferdinand.
