The invention of strong and good quality threads had a huge impact on the manner in which clothes are made. The earliest threads were organic in nature. People used leaves and bark that had been cut in very fine strips.
The basic function of the thread was to hold the clothes together to the maximum extent possible. Since bark was available very easily, breakage was not an issue. People could always stitch the clothes together again using bark or leaves from trees around them. This might have worked in the past but it cannot work today. Can you imagine civilized society today if each and every person were to walk around fearing that his or her dress may fall apart any moment?
Threads used to hold clothes together had to be very strong and yet had to be very fine and thin. A big thread would automatically be visible and would spoil the show. Thick threads cause bigger indentation during stitching. This will affect the overall life and quality of the cloth.
Unless one intends to showcase threads in a clear manner, it is understood that threads shall remain on the inside and hold the attire together without being very obvious. In such a scenario, creating thin but very strong thread became an imperative requirement of stitching.
Invention of sewing machine made it essential for threads to withstand high speed stitching processes. The needle moves in and out of the fabric at very high speeds. Further, the mechanism is such that the cloth is moved in the desired direction automatically.
The thread had to not just withstand impact but also sustain its strength over long durations. The clothes that are used are washed on an almost daily basis. Threads have to be strong enough to withstand the chemicals used to clean the attire. Stitching processes evolved only because better threads were manufactured.