Final answer:
Horizontal proliferation is the spread of weapons or weapons technology across country borders.
Step-by-step explanation:
The type of proliferation that refers to the spread of weapons or weapons technology across country borders is called Horizontal proliferation.
Horizontal proliferation occurs when weapons or weapons technology are transferred from one country to another, either through legal or illegal means. This can include the transfer of conventional weapons, such as guns and missiles, as well as weapons of mass destruction, including nuclear, chemical, and biological weapons.
Examples of horizontal proliferation include the illegal transfer of weapons technology by rogue states or terrorist organizations, as well as the legal transfer of weapons through arms deals between countries.