HIV’s spread throughout Western nations has been driven by geopolitical forces such as the ease of travel from the United States in particular, the fall of the Soviet Union and trade and migration patterns, CNN reports. Publishing their findings in ScienceDirect, researchers conducted genetic analyses of thousands of samples of HIV subtype B, the dominant subtype in the West dating back 50 years, seeking to make projections about how the virus carved paths across the Western world.

Subtype B emerged from Africa and found its way to Haiti and the United States in the decades before the scientific community first recognized the signs of AIDS in 1981. The virus’s establishment in the United States became the key that triggered the global pandemic. Travel from the United States in particular was likely instrumental in transmitting HIV to Europe, where the United Kingdom, France and Switzerland were hard-hit. Residents in those countries in turn facilitated the virus’s spread elsewhere.

HIV transmission followed different patterns in Western versus Eastern Europe. In the former region, sex between men became the dominant transmission route, while in the latter region injection drug use was the primary driver. This divide became more porous following the collapse of the Soviet Union in the early 1990s, which permitted greater travel and migration across the erstwhile Iron Curtain.

European colonialism was also instrumental in facilitating the virus’s spread.

“Our findings support the argument that epidemic control policies should be global and incorporate political and socioeconomic factors,” the study authors concluded.

To read or watch the CNN report, click here.

To read the study, click here.