Since many players ask (or complain or even question) i just try to subscibe the historical context of so called "Vandals" and their known and possible way to Spain.
That is an example that concerns every migrating people both in game and in history as it seems in most cases they were essentially the same, the only difference between them was who led the raid - not even by tribe but warchief rather and his guards/companions most probably. Those warchiefs were mostly former or even current roman officers so they knew territory, they new political situation, they used occasion to test how far usurpation (all those migration period acts should be considered as usurpation) could be evaluated until empire reacted.

There is even no single evidence the "Vandals" mentioned in sources to cross Rhein were the same who later settled in Spain. Vandalic people served in roman ranks as foederati at Danube border (some dacian/noricum locations) and most likely those are the people who moved to Spain (or joined those who theoretically crossed Rhein).
So essentially people who moved to Spain about 411 consisted of totally mixed origin, recruiting on way also whoever wanted to join. And when they settled in Spain they were eventually joined by "Alans". Those "Alans" are actually considered Iasyges who also served in roman ranks somewhere near Sirmium and called themselves "Alans" probably to gain some respect. Obviously it is likely that those Alans-Iasyges in fact contained also real Alans, so Quads and even some gothic people.

Historically "Vandals" (most likely) formed from vandalic people who served in roman ranks as foederati at Danube border, gallic roman locals (incl. settled saxonic people there) who joined them on the road, and probably some lugdunian Alans (separate ones from Alans who joined later "Vandals" in Spain) and some burgundian people, probably also serving Romans around Argentoratum.
Thus, all those migrating people should not be considered Vandals, Goths or Burgundians but gothic/vandalic/burgundian/saxonic etc. people as none of those "tribes" were homogenous nations but bands of joined raiders who apparently recognized dominacy of one "tribe" like that.

Yet significant part of vandalic people stayed in german territory (they are called in game "Lugians" which is partially truth because they were later joined by Vandals who didn't go to Spain). That is confirmed in sources that their envoys were send to Vandal king to Africa to arrange agreement over lands left in Vistula area.

So when you think of "destroying" Goths, Burgundians, Alamanns or whatever faction in game it simply doesn't mean you wiped all of them, you just removed those, who were visible on map.

Sources say that actually Suebi who emerged in Spain were consisting of bands/contingents originating in alamanic, burgundian, alan (probably quadian), longobardian and some unidentified "Buri" peoples. Later, when they settled in Spain they were joined even by significant force of Celts (or romano-celtic groups) leaving former british provinces of Rome.

Anyway sources mention that those Vandals who crossed Rhein had mortal battle vs. Franks which was eventually won with help of some unidentified alanic support. The only surrounding Alans were those living between Lugdunum and Vienna so if those Alans helped Vandals they probably were split as bunch of Alans stayed at Lugdunensis and Vienensis.
It should be then considered rather that vandalic remnants of that battle(s) were not absorbed by Alans and probably joined those unidentified Alans (as said above more probably Quads) and vandalic groups moving through southern roman borders via Raetia and Noricum. Those Vandals who moved more probable way through roman territories were not represented on map untill they came to Spain.

It seems essentially that western migration period that happened between 406-411 was inflicted with Bagaudae uprasing and mutiny in Britain rather than any "climate change" or whatever pseudo-historical/social theories say.
In that period Empire lost control of most gallic and spanish territory and that was brought into play for those germanic people who used occasion to move far from Huns. Roman territory effectively was split those days between usurpator Constantius III and rightful Empire of Honorius, divided by local upraisings of Bagaudae. Upraising was that effective enough that Stilicho were not able to counterattack usurpation held down at Alps by rebels.

Also hunnic threat didn't refer to any military actions against people at roman territory, as Huns were at peace wit west, yet hunnic chieftains considered germanic peoples who moved to roman territories as their subjects and constantly demanded them to come back under their rule so it is most probable they just wanted to be as far as possible from hunnic vincinity and possibility Romans decide to give them back to Huns.