THE arsenal discovered in the apartment of Reda Kriket, a suspected terrorist arrested on March 24th near Paris, included explosives, Kalashnikov AK-47 rifles and a machine pistol from Croatia. The terrorists who staged the attacks last November in Paris employed AK-47s made by Zastava, a Serbian manufacturer. The Kouachi brothers, who attacked the satirical magazine Charlie Hebdo the previous January, used Kalashnikov ammunition made in Bosnia. Whatever else these terrorists may have shared, one thing they certainly had in common was a fondness for Balkan arms.

The tendency of guns from the Balkans to show up in terrorist attacks in Europe is no surprise. The wars attending the breakup of Yugoslavia in the 1990s, and the near-collapse of the Albanian state in 1997, left a vast supply of small arms in the region. One study estimated the number of firearms in private hands in the Balkans at over 6m, most of them unregistered (see chart). Serbia has the highest concentration of private guns per head in Europe.

On a continent with strict gun laws, Balkan guns have been a blessing for organised crime, too. A study of 26 gang weapons seized in Marseille found nine were Kalashnikovs from the former Yugoslavia. French police report that Albanian gunrunners bring in 20 of the rifles at a time, concealed in the floors of vans. In 2014 Slovakian police stopped an entire lorry full of guns and grenades heading from Bosnia to Sweden.

Helping other regions Balkanise

Yet such shipments into north-western Europe are the small-time “ant trade” of the region’s arms industry, says Ivan Zverzhanovski, co-ordinator of SEESAC, an organisation working on small-arms control in the Balkans. The big customers are foreign governments—many of them Western. In 2014 American, Australian, British and Canadian military cargo planes collected 22m rounds of Kalashnikov ammunition and other arms from Albania and delivered them to Kurdish Peshmerga forces fighting Islamic State (IS) in northern Iraq.

In that case the munitions were free: Albania donated them to earn political credit with Washington, says Evelyn Farkas, a former American defence official. But in most cases the contracts are lucrative. Many of the militias that Western countries back in the Middle East use weapons from the former communist bloc, especially the cheap, reliable, long-lasting AK-47. Since Western countries do not make them, Balkan sources come in handy. America has been buying crates of Kalashnikovs from Serbia’s Zastava since the late 2000s, mainly for Iraqi and Afghan security forces.

Some of these guns leak into local bazaars, or are seized when militias capture government arsenals. A study by Armament Research Services (ARES) of ammunition used by IS in an area of Iraq in 2015 found that 17% of it came from the Balkans. Videos on social media show Syrian militias using Croatian rifles—almost certainly among 10,000 supplied to Iraqi forces as part of a €100m ($120m) deal in 2014-15. In 2012 Croatian arms bought by Saudi Arabia were flown to Jordan for distribution to Syrian rebels in a deal backed by the CIA.

Although most of the Balkan arms business is above-board, some is not. Non-state groups can get the “end-user certificates” needed for international deals through well-connected consultants, says one Serbian source. Another says militias in Yemen, which is under a UN arms embargo, are getting guns through buyers with end-user certificates from Persian Gulf states. Western countries that back the militias, the source says, “turn a blind eye”. Bulgarian arms supposedly destined for the Gulf are turning up in Yemen, Libya and Sudan.

Two decades after the Balkan wars ended, the region’s arms trade does not seem to be slackening. On February 19th an American air strike on an IS base in Libya killed two Serbians associated with the country’s embassy who had been kidnapped in November. Aleksandar Vucic, the Serbian prime minister, said he would rather not discuss the reasons for the kidnapping. It was, he said, “related to certain weapons deals”.

Correction: The Paris attacks in November 2015 used AK-47s made by Zastava and the Charlie Hebdo attacks used Bosnian ammunition, not the other way around. This has been corrected.