My dissertation examines how societies reach new cooperative equilibria following an exogenous shock to their structure. I seek to further our understanding of the effects cultural diversity on societal capacity to cooperate and explain why diverse and homogenous societies might choose different solutions to dilemmas of collective action. Rather than suggesting that cultural diversity has a qualitatively positive or negative impact, I propose that it creates incentives to invest in different forms of cooperation. Communities at various levels of diversity are likely to develop different social models over time. Diversity at the time of communities' inception is likely to affect what type of goods communities are better at providing and what type of rules they rely upon to maintain cooperation. I propose to study the evolution of cooperation in the Polish counties that experienced complete population turnover in the 1940-50s. In the wake of WWII, Polish borders were shifted westward, and six million people of diverse origins – over one-fifth of all Polish population – were resettled to the new territories, from which the German population was expelled. The migrants came from places as diverse as USSR, central Poland, and western and southern Europe, and in most cases had little agency in choosing their residence. Initially, dubbed "The Wild West" due to numerous social problems, the diverse post-migration societies in western and northern Poland have achieved high levels of development over time. At the same time, they demonstrate social features that differ markedly from areas without a history of migration. My dissertation aims to explain the differences between communities with different migration histories by tracing how coordination mechanisms and social norms have evolved since the formation of these communities. I plan to collect seven decades of rich archival and interview data and conduct a survey to understand how cooperative arrangements developed at the micro and macro levels.