What themes have dominated Russian history and how have they affected Russian development?
The two primary themes which have dominated Russian history has been Russia's self styled denomination as the "Third Rome" following the fall of Constantinople, and the attempts by Peter I and Catherine the Great to Westernize Russia.
Christianity came to Russia early from Byzantine Missionaries, and Russia retained a close affinity to Byzantium. The Czar often married a member of the ruling Byzantine household. Because of this relationship, Russian religion was and is Orthodox. Following the capture of Constantinople in 1453, Russian clerics referred to it as the Third Rome, the successor and only bastion of the true religion. An element of this Orthodoxy was strict obedience to the ruler, who was considered to be chosen by God. This was not exactly Divine Right; but rather an aberration of the old Byzantine doctrine of Caesaropapism. As a result, the Russian people followed the Czar without question, up until the Revolutions under Nicholas II. The only resistance to the Czar previously was from the leading Boyar families.
Russia had always been proud of its Eastern heritage, and was largely isolated from the West, in fact Louis XIV of France once sent a letter to a Russian Czar who had been dead for several years. Peter I was determined to Westernize Russia. As a result of his efforts, the capital was moved from Moscow to St. Petersburg, and Western customs and practices encouraged, including the shaving of beards and wearing western dress. Catherine the Great, his granddaughter in law, encouraged Enlightenment ideals, and even promoted the use of French at the Russian Court, a practice that continued for a number of years.
So, its attempt to Westernize and its practice of Orthodox Christianity are the two defining elements of Russian history.