This major political crisis centered on the government’s attempt to amend Japan’s security treaty with the United States to make Japan a clearly equal partner with the US. Left-wing opposition parties claimed the treaty would drag Japan into a war between the US and the communist nations. Opposition strengthened when the USSR shot down a US U-2 spy plane in early 1960, leading to increased tension between the US and the USSR. Demonstrations throughout Japan forced cancellation of a planned visit by US President Dwight D. Eisenhower, but the ruling Liberal-Democratic Party still pushed the treaty through the Diet. Later, the prime minister resigned. His successor shifted the emphasis in Japanese politics away from national security to economic development.