What was the crop-­lien system that emerged in the south and how did it shape the region after the civil war?

Crop Lien system was credit system. It became widespread among the cotton farmers in the southern regions of US. In the system the sharecroppers and tenant farmers who didn't possess land obtained supplies on credit from the local merchants, the merchants and the landowner used to get money from cotton sale and then what ever was left went to the farmer. The system ended in 1940's when the poor farmers moved to urban areas. this credit system developed during the American Civil war as the southern farmers had little cash and it was a way to get credit before the planting season. Due to the credit merchants were able to dictate the crops that farmer grew. The system was also  used by landowners, tenant farmers and sharecroppers.

to act quickly in times of danger to the united states

because you have to act quickly if you want to live/survive.