Tension may arise and violence erupt on the border between two countries as a result of any of a number of causes, including: infiltration of armed intruders from one country into the other; exchange of fire across the border; seizure of citizens of one country by agents of the other; movement of individuals from one country to the other in search of asylum or to escape imprisonment; smuggling; build-up of armed forces along a border.
Border incidents tend to occur in cases where the relations between the two countries are strained, for example: North Korea/South Korea; South Africa/Mozambique; China/Vietnam; India/Pakistan; Israel and neighbouring Arab countries; Tanzania/Uganda; India/China; Germany/Czech Republic.