By the third decade. [fact]
The force of Du Bois's work was more than the ideologues of American Marxism required and, on the other hand, more than American academic history could accept. More than two decades would pass before Black Reconstruction would again receive serious attention in either circle. By that time, Du Bois was nearing his nineties and the American Communist Party had been reduced to a sect. By the third decade, the shadow of Du Bois lay across American historiography.
Cedric J. Robinson, Black Marxism_ The Making o…, loc. 2331