Any way the first shot of the war was a murder treacherous act called the sinking of Belgrano
You need to read up on the war and the dates things happened, b787. You are flat wrong.
The two nations were fghting a war that the Argentines initially started by landing on the islands and taking them.
When they would not remove themselves, England made it clear that they would fight to take those islands back.
The Argentine cruiser, if it could get to the islands...or near the task force, could have dne great damage.
England was not going to allow that. so, it was sunk on May 2nd by a British submarine.
However, that was NOT the first act of war fighting.
That happened the day before, on May 1st when the mounted a major Argentine air strike of A-4 Skyhawks, IAI Daggers, English Electric Canberras, and Mirage III escorts who flew out on May 1st to attack ships they believed were already at the islands.
A section of Grupo 6 (flying IAI Dagger aircraft) found English ships, which were firing at Argentine defences and the Daggers managed to attack the ships and return safely. Again, that was May 1st, the day before the crusier was sunk.
As I stated, the the nuclear-powered submarine HMS Conqueror sank General Belgrano on May 2nd..
So it was not the first fighting, or major attacking. The Argentines did that the day before.
In addition, it was a mjor Argentine combatant that could have posed significant risk...and since the Argentines had already attacked English ships off of the islands, they responded by sinking that cruiser. Such are the fates of war.