Liberalism respects the quality of oneness in that all men are created equal as opposed men being born into hereditary divisions of class.  The Old Order represented a hierarchy with humans divided into monarchs, aristocrats of various distinctions, and the common people. Here were obvious divisions and plenty of them. The new order placed men on a single order at the birth--they are born equal, all alike, and in that sense, all one.  (Thereafter, in life, they are divided by their accomplishments as their lives advance, as they achieve status and rank (dubbed "meritocracy").  (Of course, 18th-century liberalism did not equalize slaves, women, and some others.  See Jefferson on race inferiority, later in the answer.)  Women, as Paine wrote in Common Sense, are different, and unequal, in the order of nature.  

But on the other hand . . . 

 As the Declaration proclaimed, the new liberal order provides/should provide for one to pursuit his personal, individual happiness.  Individualism is a bed-rock characteristic of this new U.S. No community must dictate what one's happiness must be or what one's choices must be.  Community--homogeneous, single-minded people all lumped together, all clones, is not the highest goal of liberalism.. And so, there is both oneness, briefly at birth, in liberalism and then differentiation among men too--the first at birth, the second, thereafter.  The differentiation has been labeled "meritocracy" --differences based upon achievement.

Liberalism also includes economic liberty and free markets.  One should not subordinate his property or pursuit of it (happiness) to the demands of any community.