Can't upgrade – European War 5: Empire Review

So I have everything I need to upgrade to the 4th era but it won't let me. I have all the materials, I'm above the level needed, but I can't upgrade still. It has this lock over it like I'm missing something, maybe I am but it isn't obvious to me. I'd love to progress in the game.. Please fix... I love the game and would hate for it to be ruined by this...
Review by From: nickname created on European War 5: Empire.