text: Frederick used Poland's religious dissension to keep the kingdom open to Prussian control. Poland was predominantly Roman Catholic, but approximately ten per cent of Poland's population, 600,000 Eastern Orthodox and 250,000 Protestants, were non-Catholic dissenters. During the 1760s, the dissenters' political importance was out of proportion to their numbers. Although dissenters still had substantial rights, the Polish-Lithuanian Commonwealth had increasingly been reducing their civic rights after a period of considerable religious and political freedom. Soon Protestants were barred from public offices and the  (Polish Parliament). Frederick took advantage of this situation by becoming the protector of Protestant interests in Poland in the name of religious freedom. Frederick further opened Prussian control by signing an alliance with Catherine the Great who placed Stanisław August Poniatowski, a former lover and favourite, on the Polish throne.
  After Russia occupied the Danubian Principalities in 1769–1770, Frederick's representative in Saint Petersburg, his brother Prince Henry, convinced Frederick and Maria Theresa that the balance of power would be maintained by a tripartite division of the Polish–Lithuanian Commonwealth instead of Russia taking land from the Ottomans. They agreed to the First Partition of Poland in 1772 without war. Frederick acquired most of Royal Prussia, annexing  and 600,000 inhabitants. Although Frederick's share of the partition was the smallest of the partitioning powers, the lands he acquired had roughly the same economic value as the others and had great strategic value. The newly created province of West Prussia connected East Prussia and Farther Pomerania, granted Prussia control of the mouth of the Vistula River, and cut off Poland's sea trade. Maria Theresa had only reluctantly agreed to the partition, to which Frederick sarcastically commented, "she cries, but she takes".