if you compare the United States to other nations, you can almost immediately see a significant imbalance between for example European nations to the United States of America. Europe has been plagued in conflict and only recently have had a chance to ease up border stresses, though this even today isn’t always the case for some nations in Europe. America on the other hand has had as of late internal conflict such as politics becoming a game between politicians and terrorist attacks which resulted to America furthermore developing its nation. It’s participated in wars, though hasn’t had one in its own land since the Civil War and other minor conflicts.
Hope this helps!