Question

why were the Founding Fathers were concerned about two party system

Answer 1

Today, without its two leading political parties, Democrats and Republicans, it may seem impossible to conceive of the US government. But when delegates to the Constitutional Convention met in Philadelphia in 1787 to hammer out the structure of their new government, they entirely excluded political parties from the founding document of the new nation. There was no mistake at all. The framers of the new Constitution urgently tried to stop conflicts in the bloody civil wars of the 17th century that had torn England apart. Many of them saw parties or "factions," as they called them the oppressive remnants of the British empire that they wanted to abandon in favor of a more democratic government

There is an belief that free-country parties are valuable restraints on government policy and help to keep the spirit of liberty alive. This is probably true within certain limits; and in monarchical cast governments, patriotism may look upon the party spirit with indulgence, if not with favor. Even in those of common character, it's a attitude not to be promoted in solely elective Governments.

.It is certain from their natural inclination that there will always be plenty of that spirit for any salutary reason. And, there is constant danger of excess, the aim should be to minimize and assuage it by means of public opinion. A fire not to be quenched, it requires uniform vigilance to avoid its bursting into a flame, lest it should consume instead of warming up.