Question: When did the country where the top-ranking Warsaw Pact operatives originated, despite its being headquartered in the nation known as the nobilities commonwealth, become allies with the US?

Passages:
The Polish nobility enjoyed many rights that were not available to the noble classes of other countries and, typically, each new monarch conceded them further privileges. Those privileges became the basis of the Golden Liberty in the Polish–Lithuanian Commonwealth. Despite having a king, Poland was called the nobility's Commonwealth because the king was elected by all interested members of hereditary nobility and Poland was considered to be the property of this class, not of the king or the ruling dynasty. This state of affairs grew up in part because of the extinction of the male-line descendants of the old royal dynasty (first the Piasts, then the Jagiellons), and the selection by the nobility of the Polish king from among the dynasty's female-line descendants. The Warsaw Treaty's organization was two-fold: the Political Consultative Committee handled political matters, and the Combined Command of Pact Armed Forces controlled the assigned multi-national forces, with headquarters in Warsaw, Poland. Furthermore, the Supreme Commander of the Unified Armed Forces of the Warsaw Treaty Organization which commands and controls all the military forces of the member countries was also a First Deputy Minister of Defense of the USSR, and the Chief of Combined Staff of the Unified Armed Forces of the Warsaw Treaty Organization was also a First Deputy Chief of the General Staff of the Armed Forces of the USSR. Therefore, although ostensibly an international collective security alliance, the USSR dominated the Warsaw Treaty armed forces. At the start of the war on 1 September 1939, the Allies consisted of France, Poland and the United Kingdom, as well as their dependent states, such as British India. Within days they were joined by the independent Dominions of the British Commonwealth: Australia, Canada, New Zealand and South Africa. After the start of the German invasion of North Europe until the Balkan Campaign, the Netherlands, Belgium, Greece, and Yugoslavia joined the Allies. After first having cooperated with Germany in invading Poland whilst remaining neutral in the Allied - Axis conflict, the Soviet Union perforce joined the Allies in June 1941 after being invaded by Germany. The United States provided war materiel and money all along, and officially joined in December 1941 after the Japanese attack on Pearl Harbor. China had already been in a prolonged war with Japan since the Marco Polo Bridge Incident of 1937, but officially joined the Allies in 1941.

Supporting sentences:
Despite having a king, Poland was called the nobility's Commonwealth because the king was elected by all interested members of hereditary nobility and Poland was considered to be the property of this class, not of the king or the ruling dynasty. Furthermore, the Supreme Commander of the Unified Armed Forces of the Warsaw Treaty Organization which commands and controls all the military forces of the member countries was also a First Deputy Minister of Defense of the USSR, and the Chief of Combined Staff of the Unified Armed Forces of the Warsaw Treaty Organization was also a First Deputy Chief of the General Staff of the Armed Forces of the USSR. After first having cooperated with Germany in invading Poland whilst remaining neutral in the Allied - Axis conflict, the Soviet Union perforce joined the Allies in June 1941 after being invaded by Germany.