Is this sentence right? "they had nothing more than just a poor, untrained and undisciplined militia."

Yes, your sentence is fine, in my opinion.

plot- the main storyline of a work consisting of a chain of events related by cause and effect.main plot- the main story line

it is the background information on the characters and setting explained at the beginning of the story. the exposition will often have information about events that happened before the story began. the exposition is often the very first part of the plot.