1905 Norwegian union dissolution referendum
A referendum on dissolving the union with Sweden was held in Norway on 13 August 1905. Dissolving the union, which had been in place since 1814, was approved by almost 100% of voters, with just 184 voting against the proposal out of over 371,000 votes cast.
Source: Wikipedia — 1905 Norwegian union dissolution referendum (CC BY-SA 4.0)