Countries defend their borders for two primary reasons. One is from aggression from the neighbors. The Russian invasion of Ukraine shows the violence this can cause. Fear of a Russian invasion has caused Finland to build a massive military, at least for a nation its size. The other reason is to keep out immigrants. The U.S. effort at the border of Mexico is an example of this.

The defense of borders can be very complex. A lengthy border can require large numbers of military personnel to defend it. The cost of sophisticated weapons is another consideration.

To determine the nation spending the most to defend its borders, 24/7 Wall St. ranked countries by military expenditures per land border mile. Military expenditures data is from the Stockholm International Peace Research Institute. Land border length came from the CIA World Factbook. Only 133 countries with land borders had military expenditure data. Population and land area data came from the World Bank.

The United States, with the world’s highest total military expenditure of $767.8 billion, and South Korea, which shares the world’s most tense border with North Korea, have the among the highest military expenditures per land border mile of any country on the list.

Speaking of the world’s hot spots, nations or regions involved in low-boil conflicts or shooting wars are on the list. These include the divided Mediterranean island of Cyprus, where there is an ongoing dispute between Greek Cypriots and Turkish Cypriots. More broadly, Greece and Turkey may be members of NATO, but the long-time adversaries had a recent flare-up, accusing each other of violating their air space.

Israel spends almost $34 million per mile on its borders to maintain an uneasy peace with some of its Arab neighbors, and a hostile border with others. Meanwhile, the United Kingdom’s land border is only 310 miles long, as it is mostly an island. (Several island nations did not make the list for this reason.)

Qatar, on the Arabian Peninsula, spends an eye-watering $208,382,426 per mile for its 54-mile border (the shortest we considered) with Saudi Arabia. Qatar and Saudi Arabia had been in conflict since 2017 because the Saudis claimed Doha supported terrorism.

Many NATO members are among those we considered. They have been cajoled, and sometimes browbeaten, by U.S. presidents to follow the organization’s guidelines of spending 2% of their gross domestic product on defense. One of those nations, Denmark, spends almost $59 million to protect its 87-mile border.

Also among those we considered are China, Russia and India, all of which face a daunting task of defending their extended borders. While neighboring Russia and China (each with almost 14,000 miles of border to defend) have experienced a rapprochement in recent years, border tensions between India and China have risen. India also continues to have sporadic conflicts with Pakistan over the disputed Kashmir region.

The country spending the most to defend its border is South Korea. Here are the details:

• Military expenditure per land border mile: $323,744,968 per mile (147 miles)
• Total military expenditure: $47.7 billion (ninth of 133)
• Military expenditure per land area: $1,266,212 per square miles (third)
• Land area: 37,653 square miles (85th)
• Military expenditure per capita: $919.7 per person (11th)
• Population: 51,836,239 (24th)

Methodology: To determine the country spending the most defending its borders, 24/7 Wall St. ranked countries by military expenditures per land border mile. 2021 military expenditures data is from the Stockholm International Peace Research Institute and is expressed in constant (2020) U.S. dollars. Land border length in kilometers came from the CIA World Factbook and was converted to miles. Only 133 countries with land borders had military expenditure data. All ranks are of 133.

Land area in square kilometers as of 2021 and population figures as of 2020 came from the World Bank World Development indicators. We calculated military expenditures per square miles (after conversion) of area and per capita using those figures.

It is important to note that several island countries were not considered, including Singapore, Bahrain, Malta, Japan, Seychelles and Trinidad and Tobago.

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