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 ' also provided openings for foreign diplomats to get their ways, through bribing nobles to exercise it. 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, with Russian tsars effectively choosing Polish kings. This applies particularly to the last Commonwealth King Stanisław August Poniatowski, who for some time had been a lover of Russian Empress Catherine the Great. In 1730 the neighbors of the Polish–Lithuanian Commonwealth ('), namely Prussia, Austria and Russia, signed a secret agreement to maintain the ': specifically, to ensure that the Commonwealth laws would not change. Their alliance later became known in Poland as the "Alliance of the Three Black Eagles" (or "'s Treaty"), because all three states used a black eagle as a state symbol (in contrast to the white eagle, a symbol of Poland). The Commonwealth had been forced to rely on Russia for protection against the rising Kingdom of Prussia, which demanded a slice of the northwest in order to unite its Western and Eastern portions; this would leave the Commonwealth with a Baltic coast only in Latvia and Lithuania. Catherine had to use diplomacy to win Austria to her side. The Commonwealth had remained neutral in the Seven Years' War (1756–1763), yet it sympathized with the alliance of France, Austria, and Russia, and allowed Russian troops access to its western lands as bases against Prussia. Frederick II retaliated by ordering enough Polish currency counterfeited to severely affect the Polish economy. Through the Polish nobles whom Russia controlled and the Russian Minister to Warsaw, ambassador and Prince Nicholas Repnin, Empress Catherine the Great forced a constitution on the Commonwealth at the so-called Repnin Sejm of 1767, named after ambassador Repnin, who effectively dictated the terms of that Sejm (and ordered the capture and exile to Kaluga of some vocal opponents of his policies, including bishop Józef Andrzej Załuski and others). This new constitution undid the reforms made in 1764 under Stanisław II. The ' and all the old abuses of the last one and a half centuries were guaranteed as unalterable parts of this new constitution (in the so-called "Cardinal Laws").