During the reign of Władysław IV (1632–48), the liberum veto was developed, a policy of parliamentary procedure based on the assumption of the political equality of every "gentleman", with the corollary that unanimous consent was needed for all measures.[1] A single member of parliament's belief that a measure was injurious to his own constituency (usually simply his own estate), even after the act had been approved, became enough to strike the act. Thus it became increasingly difficult to undertake action. The liberum veto also provided openings for foreign diplomats to get their ways, through bribing nobles to exercise it.[1] Thus, one could characterise Poland–Lithuania in its final period (mid-18th century) before the partitions as already in a state of disorder and not a completely sovereign state, and almost as a vassal state,[2] with Russian tsars effectively choosing Polish kings.