Why does Switzerland never participate in any of the World Wars? Reason for being one of the most peaceful country

 As others mentioned Switzerland was involved in wars until the 19th century. During both the World Wars, many European nations remained neutral - Switzerland, Sweden and Portugal among the most important. During WW-II, Turkey and Ireland, Greece, Netherlands were also neutral. 

Why was it allowed to be neutral?

Buffer state: 

Throughout history, Empires have kept buffer states between themselves and other empires. The buffer states provided the comfort for empires and put them a bit at ease & provided opportunities for diplomacy and negotation. Mongolia acted between Soviets and China, Tibet between India and China, Afghanistan, between Soviets and India, Uruguay & Paraguay between Brazil empire & Argentina, Thailand between British and French holdings in Southeast Asia. Switzerland did this role in central Europe. 

Not deliberately or socially essential: 

Hitler assaulted France out of retaliation (after WW-I) and given its long and tumultuous history. Russia was assaulted for its substantial assets and for joining the Germans in the Eastern Europe. Assaulting Switzerland had no such advantages. They were asset poor, not socially noteworthy for any nation and not amidst any real course. All things considered, the German talking parts of Switzerland were an allurement for the Nazis and the snow capped railroad/burrows had some preferred standpoint (the Swiss ensured that the warring gatherings could get to part of these assets the length of they don't take the war to their nation). 

Exceptionally brilliant military:

 Swiss were unequivocally furnished - each healthy man could battle, fixed their extensions with explosives, concealed mounted guns set on each side. Switzerland National Defense. Alongside its common protection, it had an exceptionally solid human guard. It resemble the Afghanistan of Europe, short the vital significance. Hard for any pariah to control and they ensured everybody around them understand this favorable position. It was for all intents and purposes out of question to assume control them without affecting their monetary qualities. Amid the war, Switzerland set out to shoot down German planes at whatever point they crossed Swiss airspace and opposed any endeavor by Hitler to assume control over their landing strips. 

Made concessions to both sides: Switzerland and Sweden made a considerable measure of monetary and political concessions to both sides. For both the sides, these were too significant to possibly be obliterated.