History of Switzerland
Switzerland's most important exports during the war were precision machine tools, watches, jewel bearings (used in bombsights), electricity, and dairy products. During World War Two, the Swiss franc was the only remaining major freely convertible currency in the world, and both the Allies and the Germans sold large amounts of gold to the Swiss National Bank. Between 1940 and 1945, the German Reichsbank sold 1.3 billion francs worth of gold to Swiss Banks in exchange for Swiss francs and other foreign currency.
International status and usage of the euro
There were political concerns that Serbia could use the currency to destabilise these territories (Montenegro was then in a union with Serbia) so they received Western help in adopting and using the mark (though there was no restriction on the use of the dinar or any other currency). They switched to the euro when the mark was replaced. In North Kosovo, which is mainly populated by the Serbian minority, the Serbian dinar, which replaced the Yugoslav dinar, continues to be used despite its lack of recognition or use elsewhere in Kosovo.