A couple of Swedish bands that are worth checking out. I was introduced to both when they came on tour with Maiden and they've stuck with me since.
Sabaton is a power metal band that deals almost exclusively with war themes. Their 2008 album Art of War is masterpiece that takes Sun Tzu's book and picks a period in history that exemplifies each chapter.
Ghost might seem way over the top at first glance, but they sell their performance to such an extreme that it works (at least for me). All of their videos emulate classic horror films. This song won the 2016 Grammy for Best Metal Performance: