In the early days, the possession by the Indians of the northern areas accentuated the southern connections of Illinois.  At the same time the absence at the North of navigable waterways and passable highways between East and West, left the Ohio and its tributaries the only connecting lines of travel with the remote northern Atlantic States.  Had Illinois been admitted into the Union with the boundaries first proposed, it would have been, by all those subtle influences which go to make public sentiment, a Southern State.  But the extension of the northern boundary to 42 deg. 30’ gave Illinois a frontage of fifty miles on Lake Michigan, and deflected the whole political and social history of the Commonwealth.  This contact with the great waterways of the North brought to the State, in the course of time, an immense share of the lake traffic and a momentous connection with the northern central and northern Atlantic States.  The passing of the Indians, the opening up of the great northern prairies to occupation, and the completion of the Illinois-Michigan canal made the northern part of Illinois fallow for New England seeding.  Geographically, Illinois became the connecting link in the slender chain which bound the men of the lake and prairie plains with the men of the gulf plains.  The inevitable interpenetration of Northern and Southern interests in Illinois, resulting from these contacts, is the most important fact in the social and political history of the State.  It bred in Illinois statesmen a disposition to compromise for the sake of political harmony and economic progress, a passionate attachment to the Union as the sine qua non of State unity, and a glowing nationalism.  Illinois was in short a microcosm:  the larger problems of the nation existed there in miniature.

When Illinois was admitted to the Union in 1818, all the organized counties lay to the south of the projected national road between Terre Haute and Alton, hence well within the sphere of surrounding Southern influences.  The society of Illinois was at this time predominantly Southern in its origin and characteristics.[303] Social life and political thought were shaped by Southern life and Southern thought.  Whatever points of contact there were with the outside world were with the Southern world.  The movement to make Illinois a slave State was motived by the desire to accelerate immigration from the South.

But people had already begun to come into the State who were not of Southern origin, and who succeeded in deflecting the current of Illinois politics at this critical juncture.  The fertile river bottoms and intervening prairies of southern Illinois no longer sufficed.  The new comers were impelled toward the great, undulating prairies which expand above the 39th parallel.  The rise of new counties marks the volume of this immigration;[304] the attitude of the older settlers toward it, fixes sufficiently its general social character.  This was the beginning of the “Yankee” invasion, New York and Pennsylvania furnishing the vanguard.