Final answer:
The moderate, social democratic parties dominated the Frankfurt Parliament.
Step-by-step explanation:
The political faction that dominated the Frankfurt Parliament was the moderate, social democratic parties. In the 1920s, Germans had elected moderate, social democratic governments. However, as the economic crisis deepened and Germans became increasingly desperate, they turned towards more extreme political parties like the Nazis. While the Nazis gained popularity, they never came close to winning a majority in the Reichstag.