The expansion stopped only when Russia encountered a viable threat of force from an equal power or stumbled into wars it could not win. For example, throughout the first half of the 19th century, taking advantage of the collapsing Ottoman Empire, Russia greatly expanded in the Balkans and Caucasus. Neither the international treaties signed by Russia nor the proxy wars supported by the European empires could change its behavior. When the European powers finally realized that if unchecked, the Russian forces would soon occupy the Ottoman capital, Istanbul, and control the strategic Bosporus strait, Britain and France sided with the Ottomans in a war against Russia, which became known as the Crimean War (1853-56). Russia suffered a humiliating defeat, and its ambitions in the Balkans and the Middle East were temporarily deflated.