The Soviet Union was formed in the period 1919-22, when the mainly Russian Bolshevik party took control of the former Russian empire and its vassal states. By the mid 192O's the Soviet Union extended from the Polish border to the Pacific Ocean, including annexed territories in both the West and the East. Parts of Poland and of China Mongolia were invaded and adopted into the Soviet Union. The Soviet Union continued as a political and territorial entity until 1991, when it collapsed under the pressure of nationalism in almost all the component provinces and states. Today, the strongest and most active remnant is Russia itself, with capita! Moscow. But there are other important independent countries including Ukraine, Belarus, Lithuania, Latvia, Estonia, Kazakhstan and so on.