1200-1500 words
No need to write the intro, just focus on the following outline, some adjustment can be made

AIIBs diplomatic role:
– Undermining American Plans to Establish a Political and Commercial containment around China
– Bonding with traditional U.S allies, influence US dominance role, shake US hegemony
– Prestige – Projecting Chinese National Power in the Realm of Finance
– China’s international political power bank.
What does AIIB has to do with Chinas reformist role?
– striving for a breakthrough in changing the existing international financial order.
– promote traditional MDBs to reform the development of finance and lending conditions.
Prestige –  a more assertive leadership in the financial realm. 
– sign of Chinas rising economic and financial power
n Deng Xiaopings most famous remarks: it is glorious to be rich.
Synergy BRI
– Decrease the dependence of Chinese trade tie with the US market – diversification of trade partnerships. 
– Deeper pan-Eurasian interconnection – enable the convergence of geopolitics, economic, financial, and energy interests – strategic rebalancing US
– collaboration with the Russian “ counterbalance the US
AIIB could bankroll profitable BRI projects that ultimately respond to Beijings geopolitical interests.