Having experienced two major mergers I have seen the effect of both including and excluding leadership on engagement, retention and fair treatment. Paying attention to just a few things helps set the tone.
I've captured this as "the ABC". A = Alignment; B = Behaviour; C= Culture and Conflict
A) People are going to be anxious ... grappling with all kinds of issues and differences. It's critical that leaders take the time to get and keep everyone in the organization Aligned. They've got to know where to focus and how they can make a real impact. If individuals get lost here – they may never feel included or be competitive.
B) The way leaders Behave sets the tone. It is a responsibility to make the “new world” a place where everyone wants to give everything they've got - whoever they are. Leaders should demand that team members also behave in ways that are welcoming of others, that show respect and foster great teamwork. Allowing excluding cliques and one-up groups to develop kills the opportunity to create something new and better. It also drives out of the organisation great people who are not seen as “one-of-us”.
C) There are always differences in the way people in different organisations get things done – their Cultures. It's natural to want to preserve those cultures - things people are comfortable with. Not being able to let go of some of that could be detrimental to the business. We need to be able to help people through this issue quickly and constructively. Getting bogged down arguing which approach was best for past situations is a waste. Get people focused on picking the best solutions for their collective future in the business – including ways of working together.
Few people like it - but in a stressful start-up situation – there will be Conflict. In fact there should be some as new teams test their ideas for the future. Leaders need to manage it constructively keeping the focus on resolving issues rather than company heritage, personal styles etc. Conflict needs to be addressed head on. Avoiding it poisons the new organization - just as it's starting up. If and when heritage issues start playing out unhelpfully, everyone needs a quick reminder that the competition is a) outside not inside and b) not waiting for the discussions to be completed!