Following the fall of Singapore in World War II, Australia and New Zealand both came to the realisation that Britain could no longer protect her former colonies in the Pacific. Accordingly, both countries desired an alliance with the United States and in 1951 the ANZUS Treaty was signed between the three countries. This meant that if a Treaty partner came under attack, the other two would be required to come to its aid. Although none of the ANZUS partners came under attack, (until, arguably, September 11, 2001, or the Rainbow Warrior bombing), both Australia and New Zealand nonetheless felt obliged to help America in its Cold War conflicts in Korea and Vietnam. Because of its close proximity to Asia, Australia has always been more worried than New Zealand about an invasion from Asia, and has thus been a more enthusiastic partner with America. New Zealand's contribution to the Vietnam War was small, whereas Australia went as far as to introduce conscription. By the 1970s, many people in both countries had begun to oppose the American alliance, not least because of Vietnam. America's role as a major nuclear power was also a strong factor in anti-American sentiment. In 1984 New Zealand enacted a ban on nuclear armed or powered ships in its waters, essentially preventing most American naval ships from visiting New Zealand. As a result, America suspended its treaty obligations to New Zealand under the ANZUS alliance. Despite this, New Zealand committed small numbers of soldiers to the 1991 Gulf and Afghanistan Wars, and has sent engineering units to Iraq. Australia has remained a strong supporter of America, despite major domestic opposition; it was the third largest member (by number of troops) in the 'coalition of the willing' in Iraq.