Age of Civilizations Although it may not be the most popular stradegy game on mobile devices, personally I believe it is the best. Age of civilizations is the closest concept to Hearts of Iron I have been able to find, it lacks the tech trees and depth but makes up for it with its simplisity and overall being able to conquer the world. Age of Civilizations is currently a paid app for android devises, but AoC 2 is currently being developed for IOS/ Android/ and PC. AoC 2 I have been told will be a free game to be released in August/ September. Let me know what u guys think #
Try Realpolitks Mobile by Jujubee studio for iOS or Android. They released it in the last weeks (July 20 - 27th) and it seems to be a cool and deep game for mobile, especially good for tablets. It was previously released for PC and it offers full fledged PC gameplay.