Short answers, pulled from the story.
The Helvetic Republic was a sister republic of France that existed in Switzerland between 1798 and 1803, during the French Revolutionary Wars. It replaced the Old Swiss Confederacy with a centralized state and covered most of modern Switzerland, excluding Geneva, Neuchâtel, and the old Prince-Bishopric of Basel.
The Helvetic Republic was proclaimed on the 12th of April 1798, when 121 cantonal deputies declared it "One and Indivisible." This followed the French army's complete takeover of Switzerland on the 5th of March 1798.
Peter Ochs, a magistrate from Basel, designed most of the Helvetic Republic's constitution. It created a two-chamber legislature made up of a Grand Council with 8 members per canton and a Senate with 4 members per canton, plus a 5-member executive called the Directory.
People resisted the Helvetic Republic because it ended local self-rule, imposed new taxes, centralized power, and restricted freedom of worship. Resistance was strongest in the traditional Catholic cantons, where Uri, Schwyz, and Nidwalden raised an army of about 10,000 men under Alois von Reding in 1798.
The Helvetic Republic ended on the 19th of February 1803, when the Act of Mediation abolished it and restored the cantons following talks Napoleon Bonaparte organized in Paris. It collapsed after years of instability, including the Bourla-papey uprising and the Stecklikrieg civil war of 1802, with 12 million francs of debt against a treasury that had started at 6 million.
The Swiss Confederation replaced the Helvetic Republic after the Act of Mediation on the 19th of February 1803. Switzerland reverted to a confederation of cantons, though the Republic's push for central authority later fed into the Swiss Federal Constitution of 1848.