It is clear to see that in an unequal society where there is a misallocation of wealth, the less fortunate will fight for their rights and for equality. The system ends up affecting these populations in a big way, for this reason, they end up uniting people from similar realities, such as union workers, lower middle class people, and mutual aid societies. What unites them is common interest: equality, social justice, better distribution of income, better wages, etc. The upper class society does not join this cause, because it does not generate any interest. This may affect their fortunes. That's why they tend to separate. When it comes to political parties, social interested play a important role on it too. It's always about the interests.