Complex sentence: Within months, the Soviet Union launched a war against Finland, forcing it to cede territory, including parts of the province of Viipuri to the Soviet Union in the Moscow Peace Treaty in early 1940.
Split into simpler sentences: Within months, the Soviet Union launched a war against Finland. Finland was forced to cede territory, including parts of the province of Viipuri, to the Soviet Union in the Moscow Peace Treaty in early 1940.