Why was it significant that the europeans brought cattle horses and other domesticated animals?

During the most recent ice age, from about 20,000 years ago (see Ice Ages), large mammals such as bison roam on the sub-arctic tundra of Europe and Asia. They are preyed upon by two groups of hunters, both much smaller and weaker than themselves - but both with a sufficiently developed social system to enable them to hunt and kill in packs. 

Shah Reza Khan steps down from power
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The Islamic Republic of Iran is established