This single invention, based on the very simple concept of drawing the cotton fibers through a fine-toothed comb through which the seeds could not pass, was to have an enormous impact on the Southern economy.
The most serious bottleneck in the tedious process of producing cotton had been removed.The way was now open for a dramatic expansion of the cotton industry in the US.
in the last sentence, I can't figure out why "was" and "now" are put together, and why there are two verbs, was and open?and what does the sentence mean?
'Now' can be used to mean 'at that point in time' as well as 'this point in time'. It means that from that moment on, the way was clear (open)- there was nothing to stop the expansion after that invention.