If you guys have any good further reading on the subject for me that would be great as well.
Edit: Sorry to be unclear in the question, but I'd specifically like to know of European examples.
I assume you're talking more about things like European "barbarians" and less so things like the 7th century Arab conquests?
The Arab conquests are pretty unambiguously an "invasion" or a "conquest" as they were directed and centrally organized military campaigns by a set of peoples who were, broadly speaking, familiar with the peoples they were conquering and set out to govern the territories they were going into.
They certainly involved population migrations but I haven't seen much in the way of dispute from historians that they were first and foremost a military campaign although the ideology and extent of organization of their leadership (was it a "state?" was it "Islamic"?) is more disputed.
On this topic. What are some good reads concerning the migration period? Really interested but cant find a good book on it.
Well, I would move the "migration period" back to around 300-700. 900 is a little late. This question, like all major questions regarding this period is up for debate. To my knowledge, most historians have moved away from calling it an invasion as most of the early Germanic groups coming across the Roman border were looking to settle within the Roman Empire. These movements sometimes became violent, such as at Adrianople, when the Goths were pushed by hunger. At the end of the day though, I think you need to take each example on a case by case basis rather than making a sweeping claim about each of the various Germanic peoples entering the Roman Empire.
I think the major debate now is not so much semantics as how much they contributed to the eventual fall of the Roman Empire.
Sorry if I answered your question for a period a little earlier than you asked, but the Migration Period for Europe generally refers to the end of the Roman Empire and not the very beginning of the Middle Ages.
This answer should go some way to answering your question, at least with regard to Britain.