Everyone knows the story of how the duke of Gloucester met up with Edward V's party coming from Wales to escort him to London for his coronation. The boy was lodged in the Tower and after a few months, neither he nor his brother were ever seen again.
Now what if Gloucester had run into a delay? Giving enough time for Edward V to get to London (and possibly be crowned). It doesn't have to be much to delay him - for instance, bogged down in the rain or somesuch - just to give Edward enough time to settle onto the throne. Would Richard still take up arms against a crowned king (like with Henry VI)? Or would he meekly bend the knee to his nephew?