Although DuBois initially commended Garvey's efforts, one has to question his sincerity. After all DuBois, considered the “Father of the Protest Movement,” had struggled against Booker T. Washington, and in Garvey, a supporter of the “Tuskegee idea” (racial self-help through industrial education within a racial segregated environment), he must have saw a continuation of that same battle. DuBois was at the same time developing a Pan Afrikanist program, and it is likely he viewed Garvey's program as either competition or a distraction. Also, DuBois had hoped to be the leader of Black folks. He had started the all-Black Niagara Movement but it failed; he instead ended up along with some white liberals establishing the National Association for the Advancement of Colored People (NAACP).
In contrast, Garvey, whose formal education could not match DuBois', was able to the establish the largest Black organization in history, and seemingly overnight. By 1919, the UNIA claimed to have 2 million members and 30 chapters around the world. Garvey captured the attention and imagination of the Black folks in a way that Du Bois was never able to. (Or any Black leader before or since.) I think that considering the situation and circumstances, it is reasonable to assume that jealousy was a factor in the DuBois-Garvey situation, especially given the fact of who DuBois was—the first person of Afrikan descent to earn a doctorate from American's most prestigious university, Harvard.
Garvey noted when he visited the Crisis office the absence of visible black staff. In fact, Crisis was largely white staffed; as director of publications and research, Du Bois was the only Afrikan American among its early officers. This fact would arouse Garvey's suspicious not simply about the magazine, but the NAACP in general. He told an audience the 1920 UNIA convention, "Negroes are big, not by the size of their pocketbook, not by the alien company they keep but by their being for their race. You cannot advocate 'close ranks' today and talk 'dark water' tomorrow; you must be a hundred percent Negro." This was a backhanded attack on DuBois. It is not my intention in this last sentence to suggest that Garvey struck the first insult. As to who introduced the personal venom into their relationship: it is a moot point. DuBois was a bit of a snob and initially an elitist; Garvey was an agitator with a flare for showmanship. He “Agitated, Educated and Organize!” The collision course these two men were on seemed predestine.
By 1920 Du Bois had become deeply suspicious of Garvey's methods, ideas, and motives, and published his own damning expose of Black Star Line finances in the Crisis. (Garvey accused Du Bois of paying conspirators to sabotage the Black Star Line in order to destroy his reputation.) In fact, DuBois wrote a series of articles in Crisis between 1922 and 1924 attacking Garvey's movement. W.E.B. Du Bois called Garvey the most dangerous enemy of the Negro race -- either "a lunatic or a traitor." He said Garvey "suffered from serious defects of temperament and training" and described him as " a little, fat, black man, ugly, but with intelligent eyes and a big head." Garvey countered by calling Du Bois the Negro "misleader." He said DuBois was purely and simply a white man's nigger and that he was "a little Dutch, a little French, a little Negro...a mulatto. Why in fact," Garvey wrote, "he is a monstrosity." Many people, especially Philip Randolph, accused Garvey of introducing the color prejudice of the Caribbean into the Afrikan American milieux. This is utter nonsense—where ever the white man has inhabited he has left colorism; it is a by-product of white supremacy and a very convenient divide and rule mechanism. In Afrika America, colorism is the 800-lb gorilla in the room.
Garvey suspected that Du Bois was prejudiced against him because he was a Caribbean native with darker skin but DuBois does not mention Garvey's nationality, only his complexion. This might suggest, that for DuBois, whose father was born in Haiti, Garvey's immigrant background was less of a concern, and that colorism was more a concern. Why else would DuBois refer to Garvey as 'black and ugly'? Their conflict though supported by ideological difference, was more personal than ideological. (DuBois had not yet embraced Communism.) But ultimately, it was about power and leadership. DuBois felt he was better trained and educated for leadership of the race.