Explain the process of state building and decline in eurasia over time

The Expansion of empires including the Mongols-facilitated Afro-Eurasian trade and communication as new people were drawn into conqueror's economies and trade networks.

Secondly

Empires collapsed in different regions of the world and in some areas were replaced by new imperial states, including Mongol Khanates.

Lastly

Interregional contacts and conflicts between states and empires, including the Mongols, encouraged significant technological and cultural transfers.