This paper links banking with asset prices in a dynamic macroeconomic model, to provide a simple characterization of financial instability. In contrast with historical bank runs, recent banking crises were driven by deteriorating bank assets. Hence, in contrast with bank run models, this paper focuses on the interaction of falling asset prices, bank losses, credit contraction and bankruptcies. This interaction can explain credit crunches, financial instability, and banking crises, either as fundamental or as self-fulfilling outcomes. The model distinguishes between macroeconomic and financial stability. Its simplicity helps understand balance sheet effects and delivers closed-form solutions without resorting to linearization. For instance, the critical threshold beyond which an asset price decline triggers financial instability can be related explicitly to the structural parameters of the economy.

This paper provides evidence that interbank markets are tiered rather than flat, in the sense that most banks do not lend to each other directly but through money center banks acting as intermediaries. We capture the concept of tiering by developing a core-periphery model, and devise a procedure for fitting the model to real-world networks. Using Bundesbank data on bilateral interbank exposures among 2000 banks from 1999 to 2012, we find strong evidence of tiering in the German banking system. This extent of tiering is unlikely to arise in standard random networks. Indeed, we show that bank specialization and balance sheet variables predict how banks position themselves in the interbank market. This link provides a promising avenue for understanding the formation of financial networks.