We investigate the role of networks of military alliances in preventing or encouraging wars between groups of countries. A country is vulnerable to attack if there is some fully-allied group of countries that can defeat that country and its (remaining) allies based on a function of their...

We study how the city system is affected by the possibility for the members of the same cultural diaspora to interact across different cities. In so doing, we propose a simple two- city model with two mobile cultural groups. A localized externality fosters the productivity of individuals when...