While Morse had been patiently struggling toward the completion of his invention, the nation had been growing more and more tense in its contest over slavery and State rights. As an outcome of the bitter feeling in 1846, two years after the fulfilment of Morse's scheme, Congress declared war against Mexico. The Southern slaveholders hoped by this war to gain from their weak neighbor territory favorable for the extension of slavery. For slavery had long since been dying out in the States east of the Mississippi and north of the Mason and Dixon Line and the Ohio. On the south of this natural boundary line the soil and climate were adapted to the cultivation of rice, cotton, sugar, and tobacco. These four staples of the South called for large plantations and an abundance of cheap labor always subject to the bidding of the planter. Slavery satisfied these conditions, and therefore slavery seemed necessary to the prosperity of the South. It was because the soil and climate north of this natural boundary line did not favor the use of slaves that slavery gradually died out in the North. The result was that in one section of the Union, the South, there was a pressing demand for slavery; and in the other, the North, there was none. As time wore on, it became evident that the North was growing in population, wealth, and political influence much faster than the South. Observing this momentous fact, the slaveholders feared that in the course of years Congress might pass laws unfriendly to slavery. Hence, their stubborn purpose to struggle for the extension of slavery as far as possible into the territory west of the Mississippi. [Illustration: Lincoln's Birthplace.] But in the North so powerful did the opposition to the spread of slavery to new States become, that by 1855 there was a great political party that had such opposition as its leading principle. One of its ablest and most inspiring leaders was Abraham Lincoln. He was born in Kentucky, February 12, 1809. The rough log cabin in which he first saw the light was the wretched home of a father too lazy and shiftless to work, and so ignorant that he is said not to have learned his letters until taught by his wife. Little Abe's only playmates were his sister Sarah, two years older than himself, and his cousin, Dennis Hanks, who lived in the Lincoln home. When Abe was seven years old the family moved to Indiana, and settled about fifteen miles north of the Ohio River. The journey to their new home was very tedious and lonely, for they had in some places to cut a roadway through the forest.