The Korean War began early in the morning of 25 June 1950, following the surprise invasion of the Republic of Korea by its northern neighbour, the communist Democratic People's Republic of Korea (DPRK). Numerically superior and better-equipped, the KPA crossed the 38th Parallel and rapidly advanced south, easily overcoming the inferior Republic of Korea Army (ROK). In response, the United Nations decided to intervene on behalf of South Korea, inviting member states to send forces to restore the situation. As a consequence, American ground forces were hastily deployed in an attempt to prevent the South Koreans from collapsing; however, they too were under-strength and poorly equipped, and by early August had been forced back by the KPA to an enclave around Pusan, known as the Pusan Perimeter. Key US allies—Britain, Canada and Australia—also committed forces, although these were initially limited to naval contingents and were largely viewed as token efforts in the US. Under diplomatic pressure the British agreed to deploy an infantry brigade in July, and would later dispatch a second brigade as the crisis worsened. The Canadians also agreed to provide an infantry brigade, although the first battalion would not arrive until December 1950. A total of 21 UN member states eventually contributed forces.