With a POD after 1871, have Germany and Austria, under any regimes you like, make all the right choices, with 20/20 hindsight, so as to completely maximize their combined strength. They can be under any regimes you want: Austria can be good old Austria Hungary, or a United States of Greater Austria, Germany can be the German Empire or a democratic, liberal republic. But both have to exist, and both have to be as powerful as possible, without venturing into the ASBs.
I'm thinking that close economic cooperation could help here; perhaps a customs & currency union, a beefed up Latin Monetary Union but only for Austria, Germany and a couple of other states in the German Sphere. Austria would have to be able to spend a lot more money on its army, maybe that Russian spy has a bad accident happen to him and Austrian war plans can be much better. More cooperation, integration in the command structure, better geopolitical choices. What would it take, so that in 2019, the two powers can increase their power, as much as is humanly possible, and have it endure for as long as possible?