Why did Russia threaten NATO countries with nuclear war?

Everyone in the world had started forgetting Russia and Ukraine war, but Russia's PM Putin's threat to attack Ukraine with nuclear weapons has again started the discussion of the Russia-Ukraine war all over the world.

The war between Russia and Ukraine is going on for 7 months. Russia's PM has announced the expansion of 4 of the parts win by the war in Ukraine country, Ukraine has objected to this announcement of PM Putin, America, and Europe with Ukraine Other countries have supported it.

      created by bbc.com

Russia PM Putin says that Europe wants to divide Russia with America.

Russia occupied the state from the angle of Ukraine:-
created by Indianexpress.com

In March 2022, when Russia started the war on Ukraine, then Russia was winning and there was a possibility of defeat of Ukraine, and 6 thousand soldiers of Ukraine were martyred.

Russia has occupied the Kharkiv, Luhansk, Donetsk, Republic, Kherson, and Zaporizhzhia states of Ukraine.

NATO countries and the US have helped Ukraine:-

After helping Ukraine with the help of NATO countries and America, he attacked the Russian army with more force and achieved his goal to some extent.

With the help of NATO country and the USA, the Ukrainian country's soldiers took back most of Kharkiv from the Russian occupation. The army of Ukraine started fighting with more force on the army of Russia and according to some news, the army of Russia left Kharkiv and started coming back.

Russian PM has announced the entry of 4 states won in Ukraine inside Russia:-
  1. Donetsk
  2. Republic 
  3. Kherson
  4. Zaporizhzhia
Russia has admitted 4 states, the Prime Minister of Russia is going to get the people of these 4 states to vote, on whether they want to go to Russia or not.
That voting will run from 23td, September 2022 to 27, September 2022.
                                         created by aljazeera.com
Russian PM has done a "Nuclear War Evacuation Drill" in Russia:-

"Nuclear War Evacuation Drill" means that any country is an act done before starting a nuclear war, in which there is a nuclear war, then any country is practicing how to send its citizens to a safe place.
If some news is to be believed, Putin has sent his family to the Siberian country to keep safe before the start of the nuclear war