The siege of Perekop, also known as the Perekop-Chongar Operation, was a battle of the Southern Front in the Russian Civil War from 7 to 17 November 1920. The White movement's stronghold on the Crimean Peninsula was protected by the Chongar fortification system along the strategic Isthmus of Perekop and the Syvash, from which the Crimean Corps under General Yakov Slashchov repelled several Red Army invasion attempts in early 1920. The Southern Front of the Red Army and the Revolutionary Insurgent Army of Ukraine, under the joint command of Mikhail Frunze, launched an offensive on Crimea with an invasion force four-times larger than the defenders, the White Russian Army under the command of General Pyotr Wrangel. Despite suffering heavy losses, the Reds broke through the fortifications, and the Whites were forced into retreat southwards. Following their defeat at the siege of Perekop, the Whites evacuated from the Crimea, dissolving the Army of Wrangel and ending the Southern Front in Bolshevik victory.

The Syvash or Sivash, also known as the Putrid Sea or Rotten Sea (Russian: Гнило́е Мо́ре, Gniloye More; Ukrainian: Гниле́ Мо́ре, Hnyle More; Crimean Tatar: Çürük Deñiz, is a large area of shallow lagoons on the west coast of the Sea of Azov. Separated from the sea by the narrow Arabat Spit, the water of the Syvash covers an area of around 2,560 km2 and the entire area spreads over about 10,000 km2. The Henichesk Strait is its eastern connection to the Sea of Azov. The Syvash borders the northeastern coast of the main Crimean Peninsula. Central and Eastern Syvash were registered as wetlands of Ukraine under the Ramsar Convention. Since the 2022 Russian invasion of Ukraine, the entire Syvash has been occupied by Russia.