The WT profile states he usurped the crown (in1399) - but did he really? He fought and defeated King Richard II's army in battle, later found and captured the King, who abdicated (perhaps under duress) or was deposed, and Henry IV was proclaimed King by parliament. Can we agree that that is not really usurption - was it not a legitimate way of claiming the crown back then?
Also at the end of the same sentence as "usurping": should not "the Lancaster's downfall... " read the Lancasters' (i.e. their collective) downfall?