to seize and possess (something) by force or without right
usurp a throne
to seize possession or exercise authority wrongfully from
usurpation /-ʹpaysh(ə)n/ noun
usurper noun
[Middle English usurpen via French from Latin usurpare, literally ‘to take possession of by use’, from usu (ablative of usus: see use1) + rapere to seize]