The reason that politics in Zambia is tribal is that politics everywhere is tribal. Human beings are inherently tribal, and even though our modern societies are large and cosmopolitan, we easily slip back into an “us vs them” tribal mentality in the political realm and tend to see our political opponents as enemies that threaten our way of life, and even as sub-human, evil, stupid and dangerous. Even though we may drift from identifying with various different cultural, ethnic, or political tribes, we will effortlessly assign diabolical intentions to rival tribes across the board. Unfortunately, it’s in our nature.
Same as Arab politics is tribal, both have been tribal societies for thousands of years and cannot just turn off tribal loyalties like that. Being a member of your tribe probably counts for as much importance as your religion, nationality, race, sometimes or maybe more so and in politics you tend to vote for or favour people of tribal affiliation.
This way of voting can splinter societies and probably explains why Africa and the Middle East are such basket cases. The intentions to do something good are there but tribal membership gets in the way so everything slows up or never gets done.