The libertarian perspective on immigration is often regarded as one of the core concepts of libertarian theory and philosophy. There is considerable disagreement among libertarians as to what stance towards immigration best accords with libertarian principles. Some hold that restrictions on immigration are an infringement of the rights of immigrants and other property owners and constitute a threat to individual liberty. Others maintain that open borders amount to a policy of forced integration on the part of the state, and that protecting the rights of property holders requires that present governments adopt much more discriminatory policies on who is allowed to enter a country.