Over the last 50 years the U.S. government has provided arms to a number of ostensible allies, including South Vietnam, Israel, Egypt, Saudi Arabia, and Iran. More recently, it has armed newly formed regimes in Iraq and Afghanistan, and American weapons have found their way to innumerable non-state actors aligned with American interests at one time or another.

One goal of supplying weapons is always obvious: the U.S. government wishes to empower pro-American forces (that are only sometimes democratic) and drive anti-American leaders and groups from power. However, another (sometimes primary) goal of selling weapons is to cushion the Pentagon against “shortfalls” in the budgetary process or to provide a constant flow of orders to American arms manufacturers.

Empowering American friends abroad is all well and good, and one can reasonably argue that selling arms relieves the American taxpayer of some of the burden of financing the world’s most expensive military by creating economies of scale in production. The problem is that these weapons come back to cause enormous geopolitical difficulties for the United States in the long run, even in the hands of seemingly steadfast and stable American allies.

The creation of problems for American foreign policy is not a budget-neutral proposition, and the short-term windfalls of large shipments overseas do not make up for the long-term problems that arise after the infusion of weapons into tense places abroad.

In 2013 the U.S. government exported almost $27 billion worth of weaponry, and not all of it went to countries like Canada, Australia, or the United Kingdom. Almost $1 billion went to Saudi Arabia, and $500 million went to Qatar. Some of these weapons undoubtedly made their way to the Islamic State (ISIS), while our Arab allies had few qualms about directly arming Bashar Al-Assad’s enemies in Syria.

According to the Defense Department, the fight against ISIS surpassed the $2 billion mark last spring. While most Americans agree that the war on ISIS is worth fighting, Islamic State fighters would have a much more difficult time without the high-powered weapons that require the provision American air support to our allies in the first place. ISIS has no indigenous weapons production capabilities of its own, and only the weapons captured from the American-supplied Iraqi Army and funneled through American allies allow the group to function as an effective fighting force.

At its core the conflict in Iraq and Syria is a sectarian one, and the United States has supplied weapons to both sides. On the one hand, Iraq’s Shia government and militias receive heavy American equipment – the US arms the government and gives it money, which in turn has basically relied on the militias to do any actual fighting – the same government and militias that abuse and threaten the Sunnis of western Iraq, leading many of them to prefer ISIS as the lesser of evil.

On the other hand, ISIS is the indirect recipient of an abundance of American arms, acquired either from U.S. allies in the region or by capturing them from Shia Iraqi forces. One of the most iconic images of the conflict thus far is of jubilant, M-16-wielding ISIS fighters driving columns of American Humvees after overrunning the American-supplied Iraqi forces in northern Iraq.

While it may be a boon for certain sectors of the military, for American manufacturers, and for some local economies, the budgetary impact of exporting arms to all but the surest of allies is negative. The recent fighting in Iraq and Syria is just one example of this phenomenon. Everyone knows that the anti-Soviet Afghan Mujahideen became al-Qaeda, the fight against which has cost Americans hundreds of billions of dollars.

Further examples are easy to come by, for example, the Iranian embargo. After the fall of the Shah (partly to keep the revolutionary government from attaining spare parts for all their shiny new F-14s) or the troubles that arise from the use of American-made weapons against a country’s own population, as happened on numerous occasions during the Arab Spring of 2011.

The conflicts that America has fought in the 21st century have thus far been expensive ones, and the export of American arms has fueled many of them. When arms exports come up for approval, let’s not forget the realities of the principal-agent problem. Once the money is safely in American coffers and the weapons are in the hands of others, there is little that can be done to control where they go, who uses them, or for what purpose. Oftentimes, the results are not worth the money.