Concentrate on economic development and turn Germany into the dominant economic power of Europe. Any military expendentures would be sufficient for defense. Let the others waste their wealth on over buying guns. The USSR would be hemmed in with a network of trade and military alliances and made dependant on Europe through trade manipulation.

The stagnated and deadended colonial empires of Britian a France would balanced by regularly negotiationing improved trade agreements with the nations of North & South America, and Asia.

The already excellent educational system would be given more breadth & depth and the likes of Einstein lured in with high wages and academic freedom.