War of the Nine Realms

A massive war between the Nine Realms began after the destruction of the Bifrost Bridge, causing the Asgardians' protective power over the Nine Realms to plummet. During this war the Troll Lords attacked the Dwarves, the Badoon engaged in a civil war, and the Marauders raided Vanaheim.

When the Tesseract was returned to Asgard after the War for Earth, the Bifrost Bridge was repaired and the Asgardians were able to intervene with the matters of the realms.

The Bifrost Destruction
"With the death of Laufey and Loki's attack on their world, the Frost Giants are a broken people... and yet they sense something has happened. The Troll Lords know it as well. For many millennia, they have coveted the Dwarven forges. Once they realize that Asgard cannot come to king Eitri's defense, they will strike. Despite their primitive nature, the Badoon feel our absence. Several of their clans have fallen into civil war. Their savagery and bloodlust will eventually spread from planet to planet unchallenged. And the Marauders amass near Vanaheim. Thor's destruction of the Bifrost continues to shift the balance of power across the Nine Realms... and into the worlds beyond Yggdrasil."

- Heimdall

To save Jotunheim from being destroyed by Loki, Thor destroyed the Bifrost Bridge during the Duel at the Bifrost Bridge. After the bridge was destroyed, many of the hostile beings in the Nine Realms realized that the Asgardian presence was missing. The Troll Lords took this chance to begin an onslaught against the Dwarves, seeing that Asgardian warriors could not come to king Eitri's defense. The Badoon began a civil war among their clans, having no Asgardians to intervene. The intergalactic group of bandits known as the Marauders seized the opportunity to raid Vanaheim, a realm whose main form of military came from the Asgardians.

War for Earth
When Loki was discovered to be attacking Midgard in search of the Tesseract, Odin used dark energy to send Thor to stop him.

When Thor found Loki, he came into conflict with S.H.I.E.L.D., who had taken Loki prisoner. He eventually escaped and a large scale battle erupted, uniting Thor with other skilled individuals, making him a member of the Avengers. The team fought against Loki and his army of Chitauri and successfully defeated them, giving Thor the opportunity to take the Tesseract back to Asgard, along with Loki as his prisoner.

After returning to Asgard, Thor gave the Tesseract to Heimdall so he could repair the Bifrost Bridge. After it was repaired Thor, the Warriors Three, Sif, and the entire Einherjar army were prepared for battle.

Asgardian Intervention
"To fight, to bleed, to die for those we love and cherish. To wage war on those who would kill any who cannot defend themselves. To hold back the ever-growing tide of Ragnarök that comes to calm us all. This is not our duty. It is the reason for our very existence. Since the days of Bor and Buri before him, we have protected the Nine Realms. But for too long, Asgard has been cut off from those who depend on our blood and courage for their survival. Without our light, darkness spreads. But the time of darkness is at an end. Asgard returns. And there will be Hel to pay!"

- Thor

With the Bifrost back in their possession, the Asgardians were able to help their allies in other Realms. Thor led the Einherjar army in battle, with Sif and the Warriors Three aiding in the war. To end the many battles, the Asgardians assisted in many battles. The war was ended by the Battle of Vanaheim.