These were the world's 15 weakest militaries in 2018

AP Photo/Salvador Melendez

Soldiers guard a corner in a gang-controlled neighborhood in Ilopango, El Salvador, August 31, 2015.

After nearly two decades focused on fighting terrorists and insurgents, the US has again put its focus on battling uniformed militaries, especially those of its two foremost rivals: China and Russia.

Those three countries field the world's most sophisticated and powerful militaries.

While head-to-head comparisons of military strength can be highly subjective, Global Firepower's 2018 Military Strength Ranking tries to fill that void by drawing on more than 55 factors to assign a Power Index score to 136 countries - adding Ireland, Montenegro, and Liberia to last year's list.

The ranking assesses the diversity of each country's weapons and their available manpower. Geography, logistical capacity, available natural resources, and the status of local industry are also taken into account.

While recognized nuclear powers receive a bonus, their nuclear stockpiles are not factored into the score. Landlocked countries are not docked for lacking a navy, but countries with navies are penalized if their fleets lack a mixture of ship classes that magnify a force's power.

Read more: These are the world's 20 most dangerous countries, and photos showing what life is like there

In general, a country's current political and military leadership was not considered (though NATO members got a boost) but financial health and stability are.

The top power index score is 0.0000, which is "realistically unattainable," according to Global Firepower. The closer a military is to this number, the more powerful it is.

Here are the forces that came in at the bottom of the list - the world's weakest militaries.