unfortunately, Novgorod was more focused on $$$ then conquest; And Muscovy had no money but a large (poorly trained army.)
So you can kind of see why thing turned out the way they did. If you can change the Republic of Novgorod into a monarchy (though retaining republican elements would be good.)
One thing history teaches is that it's quite easy for a rich country to tear apart one whom's head of state is elected by money hungry aristocrats. You just buy them off to elect who you want, preferably somebody weak so you can strike.