In the X-Men films, the world is shown to be comprised of humans and mutants. Magneto is a mutant and believes that a war is brewing between his kind and the human race. Magneto considers mutants to be vastly superior to humans, given their super-normal abilities. Magneto makes it his goal to separate himself and his horde of mutant followers from the rest of the world and vows to crush anything that stands in his way, even the forces led by his long time friend, Charles Xavier, who wishes to see mankind and mutants get along and work together for a better world.
Magneto is something of a revolutionary. He is comparable to the Black leader, Malcolm X whereas Charles Xavier is closer to that of Martin Luther King. Magneto has not an ounce of love in his body for the human race and doesn't believe that it possesses any redeeming qualities. This surefire hatred was certainly spawned from an early, childhood experience which marred Magneto's memory for years to come. In the first X-Men film, we learn that Magneto was separated from his family at a Nazi concentration camp in Poland. It was almost certainly here that Magneto developed his misanthropic world-view that sparked his revolutionary crusade against mankind. How, he thought, could anyone treat another living being the way these humans did? Magneto was determined to make a difference.
In the first X-Men film, Magneto hatches a plot that would turn every world leader into a mutant as they convene at a United Nations event held in New York City. In the second X-Men film, Magneto tries to use a giant machine named "Cerebro" to kill every human being on the planet. Finally, in the last X-Men film, Magneto is robbed of his power by being injected with a "cure" to the mutant "disease". In each film, Magneto tries to lead a successful revolution against humanity, but in each instance, his efforts are halted.
The conflict Magneto represents is a conflict seen in our own society. There are some groups who believe that they are better than others. These groups are determined to forge a new order of their rule over those deemed "inferior". We've seen such action in the Twentieth Century when Adolf Hitler and his Nazi forces took over the nation of Germany. So the story of Magneto is one of irony. The triggering of his hatred for mankind was inspired by men like Adolf Hitler, yet Magneto's very own actions almost emulate those of Hitler's!