This is how Maargog convinced the Drow Families to join together as a Confederation under his leadership:

Long ago when the Second Age began, the Peoples of the Known World were divided among the Circle of Kings, and the Elves were under the dominion of a single demi-goddess named Lolth (who, though she is a Queen, is still referred to as a King of the Circle).  After the First Great Invitation when the majority of Elves turned back to the Knowledge of the Most High, the Drow who were banished to the North Eastern Wildlands splintered into groups and many broke away from Lolth to worship other members of the Fallen Ones as demi-gods and goddesses.  This resulted in great strife internally for position and power among the Drow Families.

As Da'rook, the most clever of the Circle of Kings, began to bring the others back under his control, he gifted Lolth with increasing power to bring her competitors under her control. Though internal strife continued for many centuries, the Fallen Ones began to meet again in secret to discuss the terms of a unified stance against the Elves. And when Da'rook revealed his plans for unleashing an Agent of Darkness unlike any that has been before, who will be a Champion of the Dark Magic of the Undead, a new alliance was finally made within the Circle.

So Lolth began to draw her fallen competitors and the Drow Families together, at first in dreams, then with visions of destiny given through mystic priesthoods, and finally in a great counsel of the Drow Family Leaders.  Each leader, independently without knowledge of the others, was told that his or her demi-god or goddess desired a personal summons to bestow honor and vision for the future. As sacrifices were made and summons conducted, all of the Family members found themselves together in a great chamber somewhere deep within the Land of Shadows, where the Fallen Ones dwell.

Each leader was confused to see the other Drow Families in the same room, and they all despaired for a moment that this may be a contest to the death to see who was worthy.  As each drew his or her weapon and prepared spells for combat, the demi-goddess Lolth appeared, quite dramatically, and commanded them to halt.  Then, one by one, each of the other demi-gods and goddesses appeared behind their respective Drow Family member. And the leaders stood silent, in wonder of this great manifestation.

"Peoples of the Spider, hear me now," began Lolth. "Our time of struggle and internal strife is coming to an end. Behold, a new power is rising, a great power that will bring us together as one and deliver our common enemy into our hands once and for all.  And the Drow shall be the greatest among the Peoples of the World!"

Methra, worshipper of Lolth, Queen, High priestess and Matriarch of Rhomduil - the most powerful of the Drow Leaders - stepped forward and asked "Oh great Lolth, what power do you speak of?"

"It is I," answered Maargog.  None of the others had noticed that he was standing in the shadows, hidden in a grey robe.  He stepped forward and drew back the hood to reveal his face.