Crohn's disease (CD) is a long-lasting condition causing inflammation that can affect any part of the gut. The purpose of this study is to evaluate the efficacy and safety of TAK-279 versus placebo in participants with moderately to severely active Crohn's disease (CD). The main aim of this study is to learn if the 3 different doses of TAK-279 reduce bowel inflammation and ulcers in the bowel compared to the placebo after 12 weeks of treatment. Another aim is to compare any medical problems that participants have when they take TAK-279 or placebo and how well the participants tolerate medical problems. An endoscopy will be used to check the bowel for inflammation. The participants will be treated with TAK-279 for 52 weeks (1 year). During the study, participants will visit their study clinic 15 times.