First off, nice job! You've got straight gold stars!
To level up beyond Level 16, you will need to get points. You'll get those mainly by earning achievements (https://www.warzone.com/wiki/Achievements
) and winning multi-player games (https://www.warzone.com/MultiPlayer/
). You can level up indefinitely, although you will not get any rewards for leveling up past Level 54 (https://www.warlight.net/wiki/Levels
- this also lists how many points you need for each level). You can also track your own points at https://www.warzone.com/Points
Basically, if you want to start leveling up a bunch- go to the Multi-Player section and start playing open games or Quickmatch. Or create games. You're mostly done getting points from single-player.
If you're looking for more built-in single player levels to occupy your time: https://www.warzone.com/singleplayer/allbuiltin
. This has the Europe Challenge, Crazy Challenge, and Insane Challenge. The Crazy and Insane challenges will take some time (mostly the Insane) so you might enjoy them.
If you want a comprehensive list of everything you can do to level up: https://www.warzone.com/wiki/Points
Edited 11/15/2017 21:20:48