Short answers, pulled from the story.
The Helvetic Republic was a centralised state proclaimed on the 12th of April 1798 by 121 cantonal deputies after French armies overran Switzerland. It replaced the old Swiss Confederation, abolishing cantonal sovereignty and feudal rights, and lasted until the Act of Mediation on the 19th of February 1803.
The Act of Mediation, issued on the 19th of February 1803, dissolved the Helvetic Republic and restored a Swiss Confederation of nineteen cantons. Former subject territories including Aargau, Thurgau, Vaud, and Ticino became cantons with equal rights, and the Three Leagues joined as the canton of Graubünden.
Two battles were fought at Zürich in 1799. In the first, from the 4th to the 7th of June, approximately 45,000 French troops faced 53,000 Austrians; the Austrians captured the city and over 150 French guns. In the second battle, French general André Masséna surrounded the Russian force under Korsakov, took more than half his army prisoner, and inflicted over 8,000 casualties, recapturing the city.
Friedrich Freiherr von Hotze was a Swiss-born Habsburg general who commanded Austrian forces in Switzerland during 1799. He was killed on the day of the Second Battle of Zürich when Jean-de-Dieu Soult's men surprised him during an early-morning reconnaissance near the Linth River.
The Congress of Vienna in 1815 permanently recognised Swiss neutrality and fully re-established Swiss independence. At the same settlement, the territory of Switzerland was expanded for the last time with the addition of the cantons of Valais, Neuchâtel, and Geneva.
The Helvetic Republic represented both the first time Switzerland existed as a unified country and a period of French occupation and forced centralisation. For cantons like Vaud, Thurgau, and Ticino it brought political freedom from dominant neighbours, while for Bern, Schwyz, and Nidwalden it meant military defeat and occupation. In 1995, the Federal Parliament declined to hold a national celebration of the Republic's 200th anniversary.