To be more accurate, that was the Soviet Union.
On 23 June 1956 there was a revolt in Hungary, and the new government stated that they intended to leave the Warsaw Pact, and was entering negotiations with the Soviet Union to have their forces withdraw from the country. And what occurred then four months of the Soviets pretending that the Revolution had not happened, and the new leadership establishing a new government.
On 28 October the government announced that Hungary was withdrawing from the Warsaw Pact, disbanded the AVH secret police, and it would be neutral in the Cold War between NATO and the Warsaw Pact. And wanted the Soviet forces in the nation to withdraw from their nation.
And on 1 November the Soviet Union invaded Hungary. Total strength was over 31,000 soldiers with over 1,000 tanks, and within two weeks they had crushed Hungary and forced it back into being a client state once again. And the majority of the leaders of the revolution were subsequently executed.
And one of the leaders that was not executed was Sandor Kopacsi. The Chief of Police in Budapest, he ordered his officers to not fire on the protestors so long as they remained peaceful and non-violent. He reached agreements with other police departments and military officers that so long as there was no bloodshed they would not intervene. And after the revolt he was selected as Deputy Commander of the National Guard.
Arrested after the Soviets retook control, he was sentenced to life in prison. But released in the general amnesty in 1963 and he moved to Canada until 1990 where he returned after the Communist Government fell once again.