Russia had some unique problems during this period that defined it as a nation but also limited the marital choices of Romanov dynasts. Beginning with Tsar Michael, the power in the country rested with the boyar class, so Michael's and Alexis' children all married other Russians from the boyar class. Peter the Great was also married off into that class, but rebelled. He shut away his boyar wife and married a Lithuanian peasant. Peter was succeeded by the peasant, 2 of his grandsons, his daughter, and a niece. One of the grandsons, Peter III, married Catharine the Great, and her descendants tended to marry into other European dynasties.
The primary reason for the lack of intermarriage with other dynasties was Russia's extreme xenophobia, which was even evident in the reign of Nicholas II when his wife of 20 years was referred to as "the German woman".