Floyd Mayweather vs Manny Pacquiao will be the biggest fight of all time financially and the most significant this century. Evaluating the greatest ever fights is a complex variable of several factors including not only the quality and excitement of the action but the political, social and cultural undertones, the scale of expectation and outside influences. Where Money Man vs PacMan comes to rank among the most important fights in ring history will depend upon what happens that coming night in the MGM Grand Garden Arena. Here is the second of my 12 most significant fights in boxing’s history. THE FIGHT AGAINST THE NAZIS . Yankee Stadium, New York . June 22, 1938 . Joe Louis vs Max Schmeling . Joe Louis (left) knocks out Max Schmeling in the first round to win the heavyweight title on June 22, 1938 . Although Herr Hitler was trumpeting Max Schmeling as a hero of the Third Reich following his knock-out victory over Joe Louis two years earlier, the German was anti-Nazi and remained so during World War II which was imminent at the time of the re-match. Louis had come back from that shock to win the world heavyweight title by defeating James J Braddock but announced he would not consider himself the true champion until he avenged the loss to Schmeling. The fight was billed as a political war between an America struggling to emerge from the Great Depression and a Germany provoking armed conflict in Europe by annexing Austria. Yet such was Schmeling’s distaste for being exploited by Adolf Hitler’s propaganda machine – and his loyal refusal to sack his Jewish manager – that his wife and mother were refused permission to travel to New York to support him in case he defected to the U.S. The social picture was clouded further by black America’s belief in Louis as a high-profile campaigner for Civil Rights. Louis is carried by his supporters ahead of his 1938 re-match with Schmeling . A poster for the rematch (left) while Louis and Schmeling shake hands at the weigh-in ahead of their  fight . Jack Johnson vs James Jeffries . Louis, who had complacently trained on the links rather in the gym for the first fight, gave up golf and women in serious preparation for the return bout. President Franklin D Roosevelt invited Louis to the White House and told him: 'Joe, we need muscles like yours to beat the Germans.’ Louis would say: ‘The whole damned country was depending on me.’ Clark Gable, Gary Cooper and Gregory Peck were among Hollywood celebrities in the 70,000 crowd, along with FBI boss J Edgar Hoover. Louis is pictured jumping aside as Schmeling falls after the knock-out . Louis had been tactically out-thought in their first fight so decided to go for broke from the first bell. A barrage of left hooks followed by a right to the body had Schmeling doubled-up in pain and referee Arthur Donovan gave him a standing eight count. Louis switched his attack to the head, dropping Schmeling twice, and Donovan called a halt only two minutes and 40 seconds into the fight. Louis, the Brown Bomber, had fractured Schmeling’s spine with his body attacks. As the man from Brandenburg was taken to hospital the ambulance passed through Harlem and he recalled later: ‘I could the noise of crowds dancing. Bands had left the bars and were playing on the sidewalks. Everywhere was filled with celebrations and saxophones.’ Louis goes on the attack against Schmeling as he gains revenge after defeat two years earlier . Schmeling would be forcibly conscripted as a German paratrooper war but served only briefly and his resistance to Hitler made him a hero in his country for a second time, after the war. He invested in successful businesses and lived until shortly before his 100th birthday, in 2005. Louis lost his money and became a greeter at Caesars Palace in Las Vegas. His old friend Schmeling visited him there once every year until his death in 1981, when he acted as a pall-bearer at Louis’ funeral.
Floyd Mayweather Jr and Manny Pacquiao's fight will be the richest ever .
Sportsmail's Jeff Powell is counting down the ring's most significant fights .
Joe Louis' 1938 re-match with Max Schmeling is the second in the series .