Passage: Allen is soon sent on an undercover mission for the CIA, joining Vladimir Makarov in a mass shooting at an airport in Moscow, Russia. Afterwards, Makarov kills Allen, aware of his true identity, and leaves his body behind to spark a war between Russia and the United States. Outraged by an apparent American-sponsored terrorist attack, Russia retaliates by launching a surprise invasion on the East Coast of the United States. With no evidence of Makarov's involvement in the airport massacre, Task Force 141 is sent to Rio de Janeiro to capture his arms dealer, Alejandro Rojas. They succeed and learn that Makarov's nemesis is being held in a Russian gulag. They assault the gulag and rescue the prisoner: Captain Price, Soap's previous commanding officer in the SAS.Price agrees to help Task Force 141 but insists on ending the United States' war with Russia. After raiding a Russian port, Price launches a ballistic missile towards Washington, D.C. and detonates it in the upper atmosphere. The resulting EMP blast disables all electronic devices across the Eastern Seaboard, giving the Americans a much-needed advantage. Soldiers fighting in D.C. narrowly avoid a bombing run of Russian-occupied strategic structures by the United States Air Force, lighting green flares atop the White House to show that the city remains in American hands.

Question: who retaliated for a surprise invasion?
Russia