In 1613, after a devastating civil war and Polish invasions, a National Assembly was appointed the task of electing the next monarch of Russia. There was a number of candidates, including the popular leader Dmitriy Pozharskiy. In the OTL universe, Michael I of the Romanovs was elected, founding the Romanov dynasty, under the strong influence of his father, the Patriarch Filaret. This alternate history explores what might have happened if Pozharskiy had been elected instead.
In this ATL, Dmitiry Pozharskiy is crowned as tsar Dmitriy I, and is the founder of the Pozharskiy dynasty. Having interacted with the common people more than the OTL tsar, as well as having witnessed firsthand the efficiency of a militia of the common folk, Dmitriy believes in the people more than Michael I, and thus establishes the Eternal National Assembly (Vechnyy Zemskiy Sobor). Moreover, he needs parliamentary support more as he is less confident of his power. A parliamentary monarchy is established instead of the absolute monarchy of OTL Russia.
On the basis of his Second Militia, Pozharskiy creates a new regular army with the use of both voluntary recruitment and conscription, and quickly reestablishes order in Russia. This progressive system of recruitment allows Russia to not only defeat the Polish-Lithuanian Commonwealth in the Polish-Muscovite War, but also annex the former Grand Duchy of Lithuania.
Next, a series of events leads to the division of Great Britain and establishment of a very dictatorial state led by Emperor Oliver I (OTL Oliver Cromwell).
Thus, Britain is reduced to a minor European power, meanwhile Russia, Spain, Norsamveldet (a large north European state comprising Scandinavia, the Netherlands and parts of Germany), and other states expand in the absence of this strong competitor. The role that the British Empire had in OTL history is largely taken on by the Russian Empire.
A timeline of the world can be found here.