By not withdrawing its influence from the Western European countries, leading them to poverty, that had taken decades to recover from. Czech Rep., Baltic states, Slovakia, Poland, former-Yugoslavia were very developed in the beginning of the twentieth century. But then we came and swamped them in our shit.
Edit: even today you see the countries I mentioned are much behind France, Germany, UK, etc. Heck, even Eastern Germany is a shithole compared to Western Germany.