The thing to remember is that Vikings = Norsemen = Normans.
Essentially the Vikings became the Normans a couple of generations down the line, invade Normandy (ever wonder where the name came from?) and established the Franco-Norman Hegemony that took over Scandinavia, Great Britain, France, Northern Spain, The Mediterranean (including the Holy Land) and pretty much the most aggressive and expansive civilisation for 1,000 years.
The Spartans never really amounted to a hill of beans. Also - the Vikings had cavalry (well the Normans did) and cavalry armed with bows will destroy phalanx formations - that's why the late Roman empire moved away from Greco-Roman tactics.
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Overhead, the Albatross hangs motionless upon the air,
And deep beneath the rolling waves,
In labyrinths of Coral Caves,
The Echo of a distant time
Comes willowing across the sand;
And everthing is Green and Submarine
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