How is the EU able to have an open border policy among different nations?

a. Developed a plural society

b. Created a common form of money

c. Eliminated all cultural differences

d. Established a common defense organization

;)

Explanation:

An open border is a border that enables free movement of people (and often of goods) between jurisdictions with few or no restrictions on movement, that is lacking substantive border control. A border may be an open border due to intentional legislation allowing free movement of people across the border (de jure), or a border may be an open border due to a lack of legal controls, a lack of adequate enforcement or adequate supervision of the border (de facto). An example of the former is the Schengen Agreement between most members of the European Economic Area (EFTA and the EU). An example of the latter has been the border between Bangladesh and India, which is becoming controlled. The term "open borders" applies only to the flow of people, not the flow of goods and services,[1] and only to borders between political jurisdictions, not to mere boundaries of privately owned property.[2]  

Open borders are the norm for borders between subdivisions within the boundaries of sovereign states, though some countries do have controlled borders within the boundaries of the state (for example in the People's Republic of China between the mainland and the special administrative regions of Hong Kong and Macau). Open borders are also usual between member states of federations (such as the United States of America), though again in some instances movement between member states may be controlled via an internal passport system. Federations and confederations typically maintain external border controls through a collective border control system, though they sometimes have open borders with other non-member states (particularly enclaves, such as Switzerland and the European Union) through special international agreements.  

Pervasive international border control is a relatively recent phenomenon in world history. In the past, many states had open international borders either in practice or due to a lack of any legal restriction. Many authors, such as John Maynard Keynes, have identified the early 20th century and particularly World War I as the point when such controls became common.[3]  

There have been sporadic attempts to promote global open borders as a viable policy option.[4] Open borders quickly became popular after 1889.[citation needed] The International Emigration Conference held in Rome in May 1924 stated that anybody has the right to immigrate to a different country if they wanted to.[citation needed] Before the 1880s, migration to the United States was not fully controlled. During World War I it became easier for people to migrate from their country of origin to foreign countries.[citation needed] After World War II, countries were looking for many new workers, and Germany issued a guest work program to attract more people to work.[citation needed] Later, in the 1970s to 1980s strict borders were reinstated in industrialized countries.[citation needed] Currently, immigration is more restricted and harder for low-skilled and low-income people.[