Before there were countries, there were tribes. In politics, there still is. Almost everyone identifies with a particular political tribe and, if even if one’s primary tribe is not one of the two contenders for government, most also identify more strongly with one of the major tribes than the other.  

Tribes began as extended family groups, but the more successful ones cooperated with other tribes for mutual benefit. Apart from intermarriage and trade, that meant confronting enemies. Even when the Roman Empire was at its peak, parts of what is now Germany remained unconquered because the Germanic tribes (which had endless internal squabbles) would unite at critical moments to repel the Romans.   

Australia’s two main political tribes are based around the Liberal and Labor parties.