Frederick was an influential military theorist whose analysis emerged from his extensive personal battlefield experience and covered issues of strategy, tactics, mobility and logistics. Austrian co-ruler Emperor Joseph II wrote, "When the King of Prussia speaks on problems connected with the art of war, which he has studied intensively and on which he has read every conceivable book, then everything is taut, solid and uncommonly instructive. There are no circumlocutions, he gives factual and historical proof of the assertions he makes, for he is well versed in history."