Integration plans track systems. Nobody plans for two leadership teams.

I was the finance chief on two integrations. The first was small and friendly and we still got the leadership question wrong. The second was twice the size and we got it right, mostly because we had been humiliated by the first.

What the plan contains

Systems, sites, headcount, contracts, a communications calendar, and a synergy number with a date attached. All necessary. All about assets.

What determines the outcome

Whether the combined commercial leadership can make a pricing decision in one meeting. Whether the acquired side's best director believes she has a future. Whether the leader running both is seen as having a side.

None of that is in the plan, and all of it is decided in the first hundred days by accumulated small signals: whose office the meeting is in, whose systems everyone is asked to learn first, whose language becomes the default. These are not soft matters. They are the mechanism by which the synergy number is either delivered or quietly written down eighteen months later.

The three interventions worth paying for

Write the decision-rights map in month one. Not the org chart — the map of which decisions belong to whom, published. In an integration, ambiguity is not neutral; it is filled by whoever is most confident, which is usually the acquiring side, which is precisely how you lose the people you paid for.

Coach the leader holding both halves. They cannot be equidistant and cannot be seen to have a side, which is a genuinely hard behavioural problem and an unusually workable one. The work is largely about making authority visible without making it partisan.

Treat the combined leadership team as a new team. It is one. Everyone in the room is pretending it is two old ones with a new seating plan. Six months of structured team work against that is trivially cheap next to the cost of a failed integration.

On the word "culture"

In every integration I have seen, "culture clash" was doing duty for at least three specific, nameable problems: unclear decision rights, an unresolved question about which heritage's standards apply, and a group of people who had not been told whether they had a future.

Name those three and much of the culture conversation stops being mystical and starts being work.

Ambiguity in an integration is never neutral. It is always resolved in favour of whoever is most confident.