After the invasion of Poland, Switzerland mobilized its full army of 850,000 to defend their country. After the fall of France the Swiss learned of “Case Tannenbaum” or “Operation Christmas Tree” the Invasion of Switzerland for the autumn of 1940.
In 1291, the original eight Swiss cantons rallied with Swiss patriot William Tell (you know: the guy the Lone Ranger theme is named after), and declared the Rutlischwur or Rutli Oath in a meadow off Lake Lucerne. The Rutlischwur established the Swiss Confederacy which remains in place to this day.
On the same meadow, seven hundred years later on 25 July 1940, Gen Henri Guisan announced to the Swiss officer corps that they would not submit to Germany. He reminded them of the Battle of Morgarten where 1400 Swiss peasants defeated 20,000 Austrian knights and that the Swiss National Redoubt had never been conquered. He also reiterated that in accordance with their federalized constitution any surrender announcement by the decentralized Swiss government only applied to that official and those individual civilians who support them. And since the Army will never surrender they would resist to the last drop of their blood.
Hitler despised the Swiss but recognized that conquering Switzerland would be time consuming and difficult. Besides the obvious terrain issues, the Swiss army comprised 20% of the population and an additional 40% were armed in some fashion. In late 1940, Hitler delayed Case Tannebaum until after the Battle of Britain then again until after the invasion of the Soviet Union, and only finally cancelled it after the Allied landings in Normandy in 1944. From 1940 to 1944 Switzerland remained one of the few countries on continental Europe not under National Socialist domination.