When was racism as we understand it today first used as a concept? How was it different from forms of discrimination that preceded it?
Not to discourage any further answers, but you might find the FAQ on Racism to be helpful. This older post from the FAQ should be especially interesting to you:
Europe had normal diplomatic relations with non-white nations before turning explosively racist to justify their actions against all others. What happened to cause this shift? by /u/victoryfanfare