阅读下面的短文，文中有15处空白，每处空白给出4个选项。请根据短文的内容，从4个选项中选择1个最佳答案。 American civil war Historians of
the war can be divided into two schools. The first considers that it was the
unavoidable outcome of conflicting (51) between Northern and
Southern (52) . The second blames it (53)
political leaders for (54) to avert an unnecessary
war. Analysts are also divided on whether the issue of slavery
was the primary cause of the war, or a symptom of other, more (55)
differences—especially sectional interests and the doctrine of
states’ rights—between the North and South which had been developing since the
formation of the American republic. The fundamental
(56) was economic. In the early 1840s the Northern states
began the process of industrialization, modernizing their society to meet the
demands of economic change. In (57) , the slogan of Abraham
Lincoln’s Republican party, "free labour, free land, free man" encapsulated the
ideology of valuing the freedom of individuals to grasp the (58)
for economic self-advancement in a booming, expanding
society. The Southern states remained stubbornly (59)
both economically and socially. It was a backward-looking way of life
of tall white mansions on great (60) dependent on a labour
system which made slaves of approximately 4 million black Americans.
America was (61) divided by economic structure, and
was led into fratricidal(杀同胞的) warfare by a series of political clashes. The
most common cause was the future of the West. The crises over California’s
admission in 1850 and over Kansas-Nebraska in 1854 were (62)
of the divergent economic interests of North and South in relation to the
West. The North wanted free land for independent labour in the
same new territories where the South (63) to perpetuate its
traditional way of life by extending slavery. The issue was not the slavery
already practised, but the (64) of its extension
(65) the West.