Does anyone know what were the reasons of Switzerland's political isolation on the international scene after World War II and how did it manage to break out of isolation?
Since its founding, Switzerland has been somewhat isolated from the rest of Europe. That's partly because of its mountainous geography, and partly because of its fierce desire for independence, and the ability NOT to participate in what was going on in Europe at any given time (feudalism in the Middle Ages, nationalism later on).
This problem was exacerbated by World War II, in which Switzerland was officially neutral. As such, it was not part of the global effort to defeat the Nazis (not even to extent of otherwise neutral Sweden, who housed Eric Erickson, a major allied spy). And it came under suspicion, which lasts to this day, for allowing its banks to "launder" money for the Nazis that was wrongly taken from Jews.
Problems peculiar to World War II are going away, as memories of the war fades, and Switzerland makes its banks more open to the rest of the world. But it has shown little interest in joining e.g., the European Union, which houses former enemies, England, France, Germany, and Italy, among others. So it probably will remain somewhat isolated.
First of all, I would not consider Switzerland to be politically isolated.
After WWII, Switzerland got the European seat of the UN (and although it took forever for Switzerland to become a member of the UN, they have been active in many UN organizations), it was a founding member of the European Free Trade Association (EFTA), which was the competing organization to what later became the EU, it is member of the Organization for Security and Co-operation in Europe (OSCE), and will chair it again in 2014, and so on.
There have been, however, isolationist tendencies in Switzerland, prominently voiced by the Swiss People's Party (SVP/UDC). The rhetoric used by the isolationists is strongly reminiscent of the "Spiritual Defence", a state-sponsored program instituted after the Anschluss to establish a sense of Swiss-ness in the population and keep the country together as independent nation in Europe.
Switzerland was not a Radically Isolationist nation in the least, but it most definitely was politically isolationist, if only on the moderate side. This can be shown by the fact that Switzerland's isolationist tendencies caused the economy to be substantially damaged after December of 2008, after the lacking political involvement outside it's borders maintained it to be alone during this crisis. Switzerland has become less and less isolationist over the years after their founding in August 1, 1291. but due to the mountainous terrain and constant neutrality, the region is still most definitely an isolationist nation.