Short answers, pulled from the story.
Belarus and Russia established the Union State on the 8th of December 1999. This agreement followed the dismantling of a border post by Russian president Boris Yeltsin and Belarusian leader Alexander Lukashenko in mid-1995.
The 2004 Russia Belarus gas dispute began when Gazprom sought control of the Belarusian transit network after political integration efforts faltered. Supplies ceased on the 1st of January 2004 due to disagreements over pricing before a new contract was signed in June 2004.
Vladimir Putin accused Alexander Lukashenko of attempting to incorporate Belarus into Russia on the 24th of January 2020 during rising tensions. This accusation triggered Russia cutting economic subsidies for Minsk and led to accusations that Moscow used the situation to cover up broader political machinations.
By 2009 Russia accounted for approximately 48% of Belarus' external trade while Belarus made up around 6% of Russia's total commerce. These figures highlight the significant economic interdependence between the two nations despite political friction.
Vladimir Putin announced plans to station tactical nuclear operations on Belarusian ground on the 25th of March 2023. Alexander Lukashenko later refuted unification ideas stating any annexation attempt would result in war by the 12th of August 2024.