What accounts for the gap between the return on equity of US and European banks?

The return on equity of US banks is significantly higher than that of European banks. But what accounts for this gap? It may be due to: The weight of capital; if banks' balance sheet structure generates a high capital requirement, the return on their equity is lower; The return on banks’ assets; if, for example, interest rate margins are higher, the return on equity is higher; The cost of liabilities; if, for example, the weight of bonds in liabilities is higher, relative to that of deposits, the return on equity is lower. We see that the low return on equity of European banks compared with US banks is explained by: Higher capital among European banks; Higher cost of liabilities for European banks; But not lower intermediation margins in Europe.