The Regent soon replaced Bismarck as envoy in Frankfurt and made him Prussia's ambassador to the Russian Empire. In theory, this was a promotion, as Russia was one of Prussia's two most powerful neighbors. But Bismarck was sidelined from events in Germany and could only watch impotently as France drove Austria out of Lombardy during the Italian War of 1859. Bismarck proposed that Prussia should exploit Austria's weakness to move her frontiers "as far south as Lake Constance" on the Swiss border; instead, Prussia mobilised troops in the Rhineland to deter further French advances into Venetia.