What role did the economic factor play in the formation of a unified Russian state in the 14-15th century?

When creating a single state of together fragmented principalities, the economic factor played a role, but not a decisive one. There was an interest in establishing economic ties between the principalities, the abolition of customs. The political factor played an important role: the country should be united, because then it is stronger. You can create a large army to fight external opponents, danger. At that time, the main threat was posed by the Mongol yoke.