International economics is the field of study to understand the causes and consequences of economic interaction between countries. Researchers in international trade field focus on gains from trade  and factor movements (e.g., immigration, outsourcing), the impact of trade on economic growth, and effects of trade policy including tariffs, regional and multilateral trade agreements (e.g., NAFTA and WTO). International  macroeconomics deal with the balance of payments, exchange rates, and macroeconomic policies including optimum currency areas and global financial crises under the open-economy.