Cultural Clashes within Organizations

Would be curious to understand other M&A experiences, where employees of one organization felt severe culture shock upon merger with another organization. We have witnessed situations where acquisitions did not go according to plan as a result of different decision-making styles, leadership hierarchies, and change management approaches. However, has anyone experienced a situation where cultural integration was initially questionable, but eventually, the integration was deemed successful from a human capital perspective, and if so, what techniques were implemented to get to that point?