The choice of drug therapy for Crohn's disease depends on several factors, such as the severity of the condition, the sections of the bowel affected, or the patient's previous treatment history. Conventional therapy consists of a short course of corticosteroid treatment followed by azathioprine therapy. Alternatively, there are so-called advanced therapies using biologics (biotechnologically produced protein substances such as antibodies), for example mirikizumab. This study aims to investigate whether direct, early treatment with mirikizumab is more effective than the standard therapy of azathioprine in combination with corticosteroids. Following an inclusion phase, patients will be randomly assigned to either treatment with mirikizumab or azathioprine + corticosteroids. Patients in the azathioprine arm may switch to mirikizumab therapy at three time points from week 24 onwards if they do not respond adequately to azathioprine therapy. The study consists of an initial treatment period of 12 weeks (induction therapy) and a maintenance therapy period of 40 weeks. Patients in the mirikizumab arm receive 13 doses of mirikizumab. This includes initially 900 mg intravenously every 4 weeks followed by 300 mg subcutaneously. In the azathioprine arm patients receive daily administration of azathioprine tablets in combination with a steroid. Assignment to one of the two treatment options is randomised with equal probability for each of the treatment options.