Southern plantation owners in the colonial era could not depend on using in dentured servants for labor because ?

There was an uncertain supply of workers.

Explanation:

Before slavery became established in America, indentured servitude was the most favoured system to obtain cheap labor. Indentured servants were usually poor immigrants who provided free labor for a number of years in exchange for shelter and food. At the end of their contract, they were granted a plot of land and were able to become farmers. However, the supply of workers that arrived in this way was uncertain, and as the need for labor increased, other methods were employed, particularly slavery.

to act quickly in times of danger to the united states

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

in the 1800s, locomotives powered by steam made transportation faster and cheaper. the resulting rapid growth of railroads led to the connection of the atlantic and pacific railroad in oklahoma city in 1897.

in the last years of the century, the improvement of steam-based engines the expansion and growth of railroads. this growth increased when the companies started to build and expand, such as the atlantic and pacific railroad, which connected new mexico with california, and missouri with oklahoma. many of these new networks were built in oklahoma, and these changes transportation henceforward.