How would the Jotuns have made war on Asgard?

Question

In the first Thor movie, after Thor's shenanigans on Jotunheim, Laufey presents Odin with a declaration of war, and then Odin takes everyone back home to Asgard through the Bifrost.

...and then what?

Aside from Loki's secret passage, which wouldn't have remained a secret very long (and probably could have been sealed off very quickly) if someone tried to march an army through it, the only way we know of to get from Jotunheim to Asgard is the Bifrost, which is controlled from Asgard's end.

Odin seems to take the threat very seriously, seriously enough to cast Thor down to earth directly in the path of Jane's van, but what sort of threat was it really?

Can you really be worried about a war where your enemy can't reach your land to attack you?

Answer 1

The Bifrost is not the only way to reach Asgard, or the other realms, or else Asgard would have no reason to be afraid of anything.

As we see in the prologue of Thor, the Jotun are perfectly capable of reaching Midgard on their own. We can only assume they're capable of reaching the other realms as well. Similarly, in the prologue to Thor 2 we see Asgard struggling to restore order to the Nine Realms after the destruction of the Bifrost. Again, if the Bifrost was the only way to travel across realms, none of the others would have been able to cause trouble.

When, in Thor, the Jotun invade, Heimdall doesn't wonder how they got there. He wonders how they got there without him seeing them. It wasn't a matter of having Jotun arrive on Asgard; it was a matter of having them inside Asgard with no warning of their approach.

The implication is that the Bifrost is merely the most direct way to travel between realms. The other methods are more "old fashioned". That is, having the Bifrost is a strategic advantage to Asgard, allowing them to move troops into and out of the other realms directly and immediately, with exact placement and quick retreat. Imagine, for example, how pre-air-flight armies would view the ability to drop paratroopers: you could get your soldiers to their destination by boat or tank, but being able to fly them overhead and put them exactly where you want them is a huge benefit.

If only one realm - Asgard - has this strategic advantage, it would put them in exactly the position of power we see in the movies.

Answer 2

Canonically, the Jotuns have at least three ways to get their forces to Asgard;

1. Straight teleportation: At the start of Thor, they appear to be able to teleport across dimensions in much the same that the Asgradians use their Bifrost. Whether this is down to the presence of the Casket of Ancient Winters or whether the Jotuns have a bifrost of their own isn't made clear, but it's apparent that they do have their own means of travel. In the absence of the casket, they may have the ability to make use of other power sources.

2. Planetary alignment: The Jotuns may simply wait for a planetary alignment of the sort seen in Thor II. This would allow them to move from their armies from their own realm to Asgard or another neutral planet where the Asgardians have a presence.

3. Loki's passage: Odin is aware that the Ice Giants have somehow already infiltrated Asgard, somewhere close to his palace. Obviously the threat is that they'll use the same route to bring in an army.

Answer 3

Odin seems to take the threat very seriously, seriously enough to cast Thor down to earth directly in the path of Jane's van, but what sort of threat was it really?

Can you really be worried about a war where your enemy can't reach your land to attack you?

First thing first (which none of existing answers addressed), Odin neither took the threat seriously nor he worried about a war.

Asgard and Jotunheim was already at war, in a sense. Jotus were already pissed with Asgard because Asgard took Casket of Ancient Winters from them. That's also a reason why Jotunheim couldn't wage war against Asgard. Without Casket of Ancient Winters, they were simply powerless (in comparison with Asgard). So, Thor's actions and Laufrey's verbal threat didn't make a difference at all. They already wanted to crush Asgard (that's why they bothered to infiltrate Asgard initially).

Odin banished Thor to Earth because Thor disregarded moral values. He wasn't supposed to attack a powerless race. He lost his worthiness to his powers.

So, real answer to your question: Jotus didn't have a choice of waging front door war against Asgard. The problem is not transport (lots of other answers have mentioned possible ways). The real problem is: They can't win without Casket of Ancient Winters (In the end of Thor movie, they didn't march an army to Asgard. They tried to finish it with Special-Ops back door way).

Answer 4

I can't remember if in the movies anyone explicitly states that Bifrost is the only way in and out from Asgard, but in Norse mitology Bifrost is just the bridge between Asgard and Midgard (Earth), it does not connect all Nine Worlds. Jötunheimr, for example, is just a different region on the same "planet" as Asgard, and they are separated by a simple river.

As I cannot comment yet, editing for a few words about Heimdall: again, unless in the movie they clearly state the contrary, Heimdall can see everything...that happens on earth. This happens in both myths and comics, and as far I can remember, in the movie there is no one saying "Heimdall the omniscient who can see everything that happens in entire existence".