North of the 40th parallel, the vast expanse of Asia was dominated by the Russian Empire. Russia possessed a central position on the continent, and a wedge-shaped projection into Central Asia, bounded by the Caucasus Mountains and Caspian Sea on one side and the mountains of Afghanistan and Western China on the other side. To prevent Russian expansionism and achievement of predominance on the Asian continent, Mahan believed pressure on Asia's flanks could be the only viable strategy pursued by sea powers.