Complex sentence: At the time Russian infrastructure was backward and the Russian government had to invest far more than its European rivals in structural changes plus the overwhelming burdens of defense would ultimately result in an economic downfall for the Russians.
Split into simpler sentences: At the time, Russian infrastructure was backward and the Russian government had to invest far more than its European rivals in structural changes. In addition there were overwhelming burdens of defense, which would ultimately result in an economic downfall for the Russians.