via patronage rather than ideological issues, and despite criticism of the Democratas that the Nacionalistas had abandoned their platform, the Nacionalistas triumphed in the election of 13 July 1931. In the election, Roxas was reelected and returned to his position as speaker of Philippine House of Representatives. In September 1931, Japan seized the Manchuria region of China. After the Mukden incident, the leaders of both the U.S. Army and U.S. Navy started to argue in Washington that the Philippines occupied a strategical position in Asia, as naval and air bases located in the Philippines would allow any power that controlled them to dominate the South China Sea, the key sea that linked the markets of Southeast Asia to China. The prevailing opinion within the U.S. military was that the United States needed its Philippine bases to deter Japan from trying to seize control of all of East Asia. In 1933, Roxas and Osmeña flew to Washington to negotiate Filipino independence from the United States. The Americans agreed to grant the Filipinos independence, but only on the condition that the United States be allowed to retain military bases in the Philippines, a condition that led for the act to be rejected by the Philippine Congress. Quezon was late to state that the allowing of the United States to retain its bases in the Philippines would make Filipino independence no different from the independence of the Japanese sham state of Manchukuo. Senate After amendments to the 1935 Philippine Constitution were approved in 1941, Roxas was elected to the Philippine Senate, but was unable to serve until 1945 because of the outbreak of World War II. The United States was scheduled to grant the Philippines independence in 1945 while Japan started to make claims for a Greater East Asia Co-Prosperity Sphere from 1940 onward. In common with other members of the Filipino elite, Roxas started to cultivate ties with Japan as it was unclear whatever the Philippines would remain in the American sphere of influence after independence or fall into the Japanese sphere of influence. However, as the United States was planning on granting independence, ending more than 400 years of foreign rule, Filipino public opinion was hostile to the idea of the Philippines joining the Greater East Asia Co-Prosperity Sphere. Having enrolled prior to World War II as an officer in the reserves, Roxas was made liaison officer between the Commonwealth government