The article references the construction of the trans-continental railroad. Many think that this was the true motive for Douglas' opening of the Kansas Nebraska Territory as he was trying to protect the interests of his constituents in the Northwest (as it was then constituted) as well as his presidential ambitions since alternative schemes for the trans-continental railroad had it going through a more southerly route.
In addition, one of the principal reasons Kansas Nebraska became as it inflamed as it did was Douglas' concept of popular sovereignty (not really a new notion as it had been around since the 1840s) and the abolition of the Missouri Compromise, which had generally subsumed the issue of slavery in the national consciousness (excluding the Wilmot Proviso and the Compromise of 1850) since its adoption in 1820.
Kansas Nebraska was really the spark that led to the sack of Lawrence, etc. Ultimately, Douglas' ambitions were hoisted on his own petard, so to speak, during the Lincoln-Douglas Debates.