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's2018 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.

Nicaragua overall rank: 122

REUTERS/Oswaldo Rivas
Power Index rating: 2.9577
Total population: 6,025,951
Total military personnel: 13,000
Total aircraft strength: 20
Fighter aircraft: 0
Combat tanks: 84
Total naval assets: 30
Defense budget: $44.2 million

Madagascar overall rank: 123

Reuters/Siphiwe Sibeko
Power Index rating: 3.0136
Total population: 25,054,161
Total military personnel: 21,600
Total aircraft strength: 2
Fighter aircraft: 0
Combat tanks: 12
Total naval assets: 8
Defense budget: $56 million

Bosnia and Herzegovina overall rank: 124

Vanessa Vilarreal/USFOR-A Public Affairs
Power Index rating: 3.0321
Total population: 3,856,181
Total military personnel: 12,750
Total aircraft strength: 20
Fighter aircraft: 0
Combat tanks: 149
Total naval assets: 0
Defense budget: $250 million

Dominican Republic overall rank: 125

Wikimedia Commons
Power Index rating: 3.1398
Total population: 10,734,247
Total military personnel: 65,925
Total aircraft strength: 62
Fighter aircraft: 8
Combat tanks: 6
Total naval assets: 33
Defense budget: $110.85 million

Gabon overall rank: 126

REUTERS/Edward McAllister
Power Index rating: 3.2781
Total population: 1,772,255
Total military personnel: 4,850
Total aircraft strength: 24
Fighter aircraft: 6
Combat tanks: 0
Total naval assets: 10
Defense budget: $81.5 million

Namibia overall rank: 127

Navy/EOD Technician 1st Class Tyler Brooks
Power Index rating: 3.5441
Total population: 2,484,780
Total military personnel: 15,500
Total aircraft strength: 31
Fighter aircraft: 6
Combat tanks: 10
Total naval assets: 8
Defense budget: $120 million

Panama overall rank: 128

REUTERS/Carlos Jasso
Power Index rating: 3.7436
Total population: 3,753,142
Total military personnel: 34,000
Total aircraft strength: 27
Fighter aircraft: 0
Combat tanks: 0
Total naval assets: 20
Defense budget: $145 million

Mauritania overall rank: 129

REUTERS/Mal Langsdon
Power Index rating: 3.7474
Total population: 3,758,571
Total military personnel: 20,870
Total aircraft strength: 26
Fighter aircraft: 0
Combat tanks: 35
Total naval assets: 5
Defense budget: $39.1 million

Central African Republic overall rank: 130

REUTERS/Camille Lepage
Power Index rating: 3.7667
Total population: 5,625,118
Total military personnel: 5,825
Total aircraft strength: 4
Fighter aircraft: 0
Combat tanks: 4
Total naval assets: 0
Defense budget: $18.5 million

El Salvador overall rank: 131

Reuters
Power Index rating: 3.7741
Total population: 6,172,011
Total military personnel: 47,000
Total aircraft strength: 52
Fighter aircraft: 0
Combat tanks: 0
Total naval assets: 4
Defense budget: $165 million

Somalia overall rank: 132

Thomson Reuters
Power Index rating: 4.0425
Total population: 11,031,386
Total military personnel: 15,900
Total aircraft strength: 25
Fighter aircraft: 0
Combat tanks: 140
Total naval assets: 3
Defense budget: $58.96 million

Sierra Leone overall rank: 133

Reuters
Power Index rating: 4.7266
Total population: 6,163,195
Total military personnel: 10,750
Total aircraft strength: 5
Fighter aircraft: 0
Combat tanks: 2
Total naval assets: 10
Defense budget: $13.04 million

Suriname overall rank: 134

Reuters / Ranu Abhelakh
Power Index rating: 5.1689
Total population: 591,919
Total military personnel: 2,270
Total aircraft strength: 3
Fighter aircraft: 0
Combat tanks: 0
Total naval assets: 3
Defense budget: $67.4 million

Liberia overall rank: 135

Stringer/Reuters
Power Index rating: 5.5241
Total population: 4,689,021
Total military personnel: 1,500
Total aircraft strength: 0
Fighter aircraft: 0
Combat tanks: 0
Total naval assets: 0
Defense budget: $10 million

Bhutan overall rank: 136

REUTERS/Singye Wangchuk
Power Index rating: 7.5497
Total population: 758,288
Total military personnel: 75,000
Total aircraft strength: 2
Fighter aircraft: 0
Combat tanks: 0
Total naval assets: 0 (landlocked)
Defense budget: $10 million