Why did political parties form?

Political parties as we know them did not begin to develop until the late 1600s. The ancient Greeks, who were pioneers in developing democracy, had no organized political parties in the modern sense. The senate of the ancient Romans had two groups that represented people with different interests - the Patricians and the Plebeians. The Patricians represented noble families. The Plebeians represented the wealthy merchants and the middle class. Although these two groups often mingled, at times they voted as factions, or parties, on particular issues that were important to the groups they represented.

Political parties formed because they had different agreements for example the republicans are against gay marriage and democrats are for gay marriage you know ...