Researchers have found that even international mergers are popular, they usually fail for its complexity. Recently few studies have tried with process perspective to penetrate into merger integration without much success. We argue that focus on pre-and post-merger stages is good but not enough to provide a total picture of the process. By using a longitudinal approach this study analyzes the establishment, development and consolidation of a cross-border merger between banks from four countries. Based on theories on strategic motives and culture, a theoretical framework has been developed showing how merger process can lead to better competitiveness and performance. Data has been collected through semi-structured interviews with officials from the merging firms, and secondary materials during 1997-2015. The merger is described in four stages. The first stage deals with the initiation and establishment of the merger. Critical period and cultural clashes are covered in the next stage. The third stage concentrates on the development of synergy. The final stage reflects on how the process has consolidated and what result it has so far achieved.