Vietnam War and resistance to the draft
In 1964, Ali failed the U.S. Armed Forces qualifying test because his writing and spelling skills were sub-par (he was quoted as saying, “I said I was the greatest, not the smartest!”). However, in early 1966, the tests were revised and Ali was reclassified as 1A. This classification meant he was now eligible for the draft and induction into the United States Army during a time when the U.S. was involved in the Vietnam War.
When notified of this status, Ali declared that he would refuse to serve in the Army and publicly considered himself a conscientious objector. Ali stated: “War is against the teachings of the Holy Qur’an. I’m not trying to dodge the draft. We are not supposed to take part in no wars unless declared by Allah or The Messenger. We don’t take part in Christian wars or wars of any unbelievers.” More succinctly and famously he said, “I ain’t got no quarrel with them Viet Cong – no Viet Cong ever called me Nigger.” The statement articulated, for many people, a reason to oppose the war.
Appearing for his scheduled induction into the U.S. Armed Forces on April 28, 1967 in Houston, Ali refused three times to step forward at the call of his name. An officer warned him he was committing a felony punishable by five years in prison and a fine of $10,000. Once more, Ali refused to budge when his name was called. As a result, he was arrested. On the same day the New York State Athletic Commission suspended his boxing license and stripped him of his title. Other boxing commissions followed suit. Ali would not be able to obtain a license to box in any state for over three years.
In the years between the appellate court decision and the Supreme Court verdict, Ali remained free. As public opinion began turning against the war and the Civil Rights movement continued to gather momentum, Ali became a popular speaker at colleges and universities across the country, rare if not unprecedented for a boxer. At Howard University, for example, he gave his popular “Black Is Best” speech to 4,000 cheering students and community intellectuals, after he was invited to speak by sociology professor Nathan Hare on behalf of the Black Power Committee, a student protest group.
On June 28, 1971, the Supreme Court in Clay v. United States overturned Ali’s conviction by a unanimous 8-0 decision (Justice Thurgood Marshall did not participate). The decision was not based on, nor did it address, the merits of Ali’s claims per se; rather, the Court held that since the Appeal Board gave no reason for the denial of a conscientious objector exemption to Ali, and that it was therefore impossible to determine which of the three basic tests for conscientious objector status offered in the Justice Department’s brief that the Appeals Board relied on, Ali’s conviction must be reversed.
Impact of Ali’s stance
Ali’s example inspired countless black Americans and others. New York Times columnist William Rhoden wrote, “Ali’s actions changed my standard of what constituted an athlete’s greatness. Possessing a killer jump shot or the ability to stop on a dime was no longer enough. What were you doing for the liberation of your people? What were you doing to help your country live up to the covenant of its founding principles?” 
Recalling Ali’s anti-war position, Kareem Abdul-Jabbar said: “I remember the teachers at my high school didn’t like Ali because he was so anti-establishment and he kind of thumbed his nose at authority and got away with it. The fact that he was proud to be a Black man and that he had so much talent … made some people think that he was dangerous. But for those very reasons I enjoyed him.”
Ali inspired Martin Luther King, Jr., who had been reluctant to address the Vietnam War for fear of alienating the Johnson Administration and its support of the civil rights agenda. Now, King began to voice his own opposition to the war for the first time.
In speaking of the cost on Ali’s career of his refusal to be drafted, his trainer Angelo Dundee said, “One thing must be taken into account when talking about Ali: He was robbed of his best years, his prime years.”
Ali’s resistance to the draft was covered in the 2013 documentary The Trials of Muhammad Ali.