The Battle of Alderaan was one of several armed conflicts revolving around the Alderaan system during the Clone Wars.
Around 20 BBY, the Trade Federation had gathered warships in the Alderaan system. These were not enough to launch a full-scale invasion of Alderaan, but enough to harass any convoys attempting to send aid. As a result of this, a convoy sending vital goods to Alderaan was put under the protection of a Republic task force, specifically aimed at engaging any Separatist forces that tried to stop them. However, due to Alderaan's insignificant military capabilities, they depended upon the Republic forces to do battle alone, and all Jedi fighters were told to spread out and engage enemy fighters as soon as they exited hyperspace, drawing their fire away from the convoy.
Right before the convoy prepared to jump into hyperspace, one of the Jedi starfighters was infiltrated and hijacked by Padawan Flynn Kybo, looking to link up with a small group of Jedi plotting to assassinate General Grievous on their own.
The outcome of the battle appeared to be a victory for the Republic, as Alderaan was said to have been "threatened", not "conquered", by the CIS, yet the horrors of the Clone Wars was enough for the Alderaanians to dismantle what little military capability they had after the war. Though they publicly claimed to have no weapons left, they actually put their arsenal on board the unmanned Alderaanian War Frigate Another Chance, which was left to jump through hyperspace unless recalled by the Alderaanian Council of Elders.