The earliest known cultural tribes of the area were members of the Hallstatt and La Tène cultures, named after the archaeological site of La Tène on the north side of Lake Neuchâtel. La Tène culture developed and flourished during the late Iron Age from around 450 BC, possibly under some influence from the Greek and Etruscan civilisations. One of the most important tribal groups in the Swiss region was the Helvetii. Steadily harassed by the Germans, in 58 BC the Helvetii decided to abandon the Swiss plateau and migrate to western Gallia, but Julius Caesar's armies pursued and defeated them at the Battle of Bibracte, in today's western France, forcing the tribe to move back to its original homeland. In 15 BC, Tiberius, who was destined to be the second Roman emperor and his brother, Drusus, conquered the Alps, integrating them into the Roman Empire. The area occupied by the Helvetii—the namesakes of the later Confoederatio Helvetica— first became part of Rome's Gallia Belgica province and then of its Germania Superior province, while the eastern portion of modern Switzerland was integrated into the Roman province of Raetia. Sometime around the start of the Common Era, the Romans maintained a large legionary camp called Vindonissa, now a ruin at the confluence of the Aare and Reuss rivers, near the town of Windisch, an outskirt of Brugg.
The first and second century AD were an age of prosperity for the population living along the Swiss plateau. Several towns, like Aventicum, Iulia Equestris and Augusta Raurica, reached a remarkable size, while hundreds of agricultural estates (Villae rusticae) were founded in the countryside.
In about 260 AD, the fall of the Agri Decumates territory north of the Rhine transformed today's Switzerland into a frontier land of the Empire. Repeated raids by the Alamanni tribes provoked the ruin of the Roman towns and economy, forcing the population to find shelter near Roman fortresses, like the Castrum Rauracense near Augusta Raurica. The Empire built another line of defense at the north border (the so-called Donau-Iller-Rhine-Limes), but at the end of the fourth century the increased Germanic pressure forced the Romans to abandon the linear defence concept, and the Swiss plateau was finally open to the settlement of German tribes.
In the Early Middle Ages, from the end of the 4th century, the western extent of modern-day Switzerland was part of the territory of the Kings of the Burgundians. The Alemanni settled the Swiss plateau in the 5th century and the valleys of the Alps in the 8th century, forming Alemannia. Modern-day Switzerland was therefore then divided between the kingdoms of Alemannia and Burgundy. The entire region became part of the expanding Frankish Empire in the 6th century, following Clovis I's victory over the Alemanni at Tolbiac in 504 AD, and later Frankish domination of the Burgundians.
Throughout the rest of the 6th, 7th and 8th centuries the Swiss regions continued under Frankish hegemony (Merovingian and Carolingian dynasties). But after its extension under Charlemagne, the Frankish empire was divided by the Treaty of Verdun in 843. The territories of present-day Switzerland became divided into Middle Francia and East Francia until they were reunified under the Holy Roman Empire around 1000 AD.
By 1200, the Swiss plateau comprised the dominions of the houses of Savoy, Zähringer, Habsburg, and Kyburg. Some regions (Uri, Schwyz, Unterwalden, later known as Waldstätten) were accorded the Imperial immediacy to grant the empire direct control over the mountain passes. With the extinction of its male line in 1263 the Kyburg dynasty fell in AD 1264; then the Habsburgs under King Rudolph I (Holy Roman Emperor in 1273) laid claim to the Kyburg lands and annexed them extending their territory to the eastern Swiss plateau.
Switzerland was not invaded during either of the world wars. During World War I, Switzerland was home to Vladimir Illych Ulyanov (Vladimir Lenin) and he remained there until 1917. Swiss neutrality was seriously questioned by the Grimm–Hoffmann Affair in 1917, but it was short-lived. In 1920, Switzerland joined the League of Nations, which was based in Geneva, on the condition that it was exempt from any military requirements.
During World War II, detailed invasion plans were drawn up by the Germans, but Switzerland was never attacked. Switzerland was able to remain independent through a combination of military deterrence, concessions to Germany, and good fortune as larger events during the war delayed an invasion. Under General Henri Guisan central command, a general mobilisation of the armed forces was ordered. The Swiss military strategy was changed from one of static defence at the borders to protect the economic heartland, to one of organised long-term attrition and withdrawal to strong, well-stockpiled positions high in the Alps known as the Reduit. Switzerland was an important base for espionage by both sides in the conflict and often mediated communications between the Axis and Allied powers.
Switzerland's trade was blockaded by both the Allies and by the Axis. Economic cooperation and extension of credit to the Third Reich varied according to the perceived likelihood of invasion and the availability of other trading partners. Concessions reached a peak after a crucial rail link through Vichy France was severed in 1942, leaving Switzerland completely surrounded by the Axis. Over the course of the war, Switzerland interned over 300,000 refugees and the International Red Cross, based in Geneva, played an important part during the conflict. Strict immigration and asylum policies as well as the financial relationships with Nazi Germany raised controversy, but not until the end of the 20th century.
During the war, the Swiss Air Force engaged aircraft of both sides, shooting down 11 intruding Luftwaffe planes in May and June 1940, then forcing down other intruders after a change of policy following threats from Germany. Over 100 Allied bombers and their crews were interned during the war. During 1944–45, Allied bombers mistakenly bombed a few places in Switzerland, among which were the cities of Schaffhausen, Basel and Zürich.
After the war, the Swiss government exported credits through the charitable fund known as the Schweizerspende and also donated to the Marshall Plan to help Europe's recovery, efforts that ultimately benefited the Swiss economy.
During the Cold War, Swiss authorities considered the construction of a Swiss nuclear bomb. Leading nuclear physicists at the Federal Institute of Technology Zurich such as Paul Scherrer made this a realistic possibility. However, financial problems with the defense budget prevented the substantial funds from being allocated, and the Nuclear Non-Proliferation Treaty of 1968 was seen as a valid alternative. All remaining plans for building nuclear weapons were dropped by 1988.
Switzerland was the last Western republic to grant women the right to vote with some Swiss cantons approving this in 1959, and later with a federal level in 1971 and, after resistance, in the last canton Appenzell Innerrhoden (one of only two remaining Landsgemeinde) in 1990. After suffrage at the federal level, women quickly rose in political significance, with the first woman on the seven member Federal Council executive being Elisabeth Kopp, who served from 1984–1989, and the first female president being Ruth Dreifuss in 1999.
Switzerland joined the Council of Europe in 1963. In 1979 areas from the canton of Bern attained independence from the Bernese, forming the new canton of Jura. On 18 April 1999 the Swiss population and the cantons voted in favour of a completely revised federal constitution.
In 2002 Switzerland became a full member of the United Nations, leaving the Vatican City as the last widely recognised state without full UN membership. Switzerland is a founding member of the EFTA, but is not a member of the European Economic Area. An application for membership in the European Union was sent in May 1992, but not advanced since the EEA was rejected in December 1992 when Switzerland was the only country to launch a referendum on the EEA. There have since been several referenda on the EU issue; due to a mixed reaction from the population the membership application has been frozen. Nonetheless, Swiss law is gradually being adjusted to conform with that of the EU, and the government has signed a number of bilateral agreements with the European Union. Switzerland, together with Liechtenstein, has been completely surrounded by the EU since Austria's membership in 1995. On 5 June 2005, Swiss voters agreed by a 55% majority to join the Schengen treaty, a result that was regarded by EU commentators as a sign of support by Switzerland, a country that is traditionally perceived as independent and reluctant to enter supranational bodies.