Boundaries Government policy 3 History 3 Smuggling 3 Border patrols 2 Colonies 2 Commerce 2 more ... Drug control 2 Economic conditions 2 Illegal immigration 2 Noncitizens 2 Basic income 1 Border security 1 Commercial policy 1 Conservation of natural resources 1 Counterfeits and counterfeiting 1 Cultural fusion 1 Differentiation (Sociology) 1 Dominance (Psychology) 1 Drug traffic 1 Emigration and immigration 1 Environmental aspects 1 Ethnic relations 1 Globalization 1 Greeks 1 Illegal arms transfers 1 Imperialism 1 Income 1 International trade 1 Interstate commerce 1 less ...