Would is used to denote something that we now know took place after something else. The year is 2010 now and the text describes events that unfolded earlier. If the reference were to the future, the year 2015 for example, we would say: It will invade the Ruatoki Valley in 2015.
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Cool BreezeWould is used to denote something that we now know took place after something else.So using "would invade",instead of "invaded",adds a bit more "assertive tone" to a known fact.