Which States Enter into Treaties, and Why?

Treaties are the primary source of international law. But little is known about which countries enter into treaties, which forms the treaties take, and which subjects they address. We present an exploratory analysis of a unique dataset of roughly 50,000 treaties ratified since 1946. We hypothesize that states enter treaties in order to obtain public goods but that the transaction costs of negotiating and enforcing treaties also limit the value of treaties. Simple predictions are that larger and richer states should benefit more from cooperation: therefore, they should be parties to more treaties. Older, less corrupt, and (again) larger states should face lower transaction costs and should belong to more treaties. Consistent with this prediction, these states enter into more bilateral treaties and "closed" multilateral treaties, but universal multilateral treaties where the benefits of cooperation are more attenuated and the costs of negotiation are low for small states.