Hadrian, the Roman emperor, journeyed to Athens in spring of AD 125 for the Great Dionysia, one of the most important festivals in the Hellenic world honouring Dionysus, the patron deity of theatre and wine. 

As ruler of the Roman empire, Hadrian could attend in imperial regalia, wearing a purple toga embroidered with gold threads, or take part as a local patron, adopting the customs and symbols of the city. He chose the latter, showing up as one of the officials in charge, presiding over the celebrations while dressed in a simple white cloth worn by Athenian citizens. 

In doing so, he didn’t erase differences between Roman and Greek culture – he created a bridge between them.

Modern mergers and acquisitions present a similar challenge. Leaders often approach cultural integration as a problem to be solved through structural alignment and standardisation. Yet decades of research on post-merger integration shows that employees experience mergers through the lens of values, identity and purpose. This is why cultural integration so often becomes the decisive factor in whether a merger deal succeeds.

When integration fails, it’s rarely because leaders ignore culture altogether. More often, it’s because they focus on the wrong aspects of it. We outline three common mistakes and our recommendations for avoiding them.

Mistake 1: Confusing equal power with fairness

One of the most common concerns in M&A is that the acquiring company will dominate the acquired company’s culture, leading to conflict. To avoid such “winner vs. loser” dynamics, many mergers are framed as “mergers of equals”. 

The creation of Citigroup in 1998 through the merger of Citicorp and Travelers Group illustrates both the intent and limits of this approach. Citigroup adopted a highly symmetrical structure, with two co-CEOs, equal board representation and shared decision-making authority. The CEOs shared veto power over strategic decisions, meaning that all significant decisions had to be made jointly. 

Although this arrangement divided power equally between executives, it didn’t address the need to create a workable governance structure and fair corporate environment. In practice, the structure diffused authority, while unclear decision rights made coordination more difficult and amplified strategic tensions. A decade later, the merger was regarded by some as one of the worst of all time. 

In contrast, when Indosat Ooredoo and Hutchison Tri Indonesia merged in 2022, leadership placed strong emphasis on ensuring that decisions were transparent, consistent and grounded in clear criteria. This was particularly important in the restructuring process. Rather than relying on informal judgments, the organisation adopted data-driven assessments and involved independent third parties to evaluate employees. Even difficult decisions such as redundancies were broadly accepted by employees, thanks to the clarity and consistency of the process.

Our recommendation: Be fair and transparent, because this is what employees expect. Research suggests that clear decision rights, objective evaluation processes and perceived fairness are key to building trust and fostering employee engagement post-M&A.

Mistake 2: Confusing espoused values with lived ones

Cultural integration often focuses on aligning values. Leaders invest significant effort in defining shared principles, integrating them into communications and codifying them in formal documents. Yet alignment on paper doesn’t guarantee alignment in practice.

Take the 1999 merger of MindSpring and EarthLink, both internet service providers (ISPs) in the United States. MindSpring was known for a strong values-driven culture. The company’s "Core Values and Beliefs" such as respect, integrity and customer focus were distributed to employees and guided everyday decisions. Executives from EarthLink were sufficiently impressed that they incorporated these into the combined corporate handbook. 

However, while the language of customer focus and respect remained, operational choices at the merged company emphasised efficiency. The issue wasn’t the absence of values but the inconsistency in how they were enacted, a gap that research shows could be read by employees as an integrity problem and erode their trust and commitment.

Initially, the combined company became the second-largest ISP in the US, with nearly 3 million subscribers and peaking at 5 million in 2004. But operational friction eventually caused it to miss the transition to broadband. By 2007, it was forced to cut 900 jobs, and by mid-2009, its subscriber base had halved.

Our recommendation: Align behaviour, not just values. Leaders must ensure that behaviours are grounded in the principles they champion. Values only shape culture when they are reflected in everyday decisions.

Mistake 3: Confusing cultural differences with strategic incompatibility

Two organisational cultures are rarely fully aligned and friction is inevitable. The challenge for leaders is not to eliminate these differences, but to determine which ones matter.

Consider an anonymised example of two software companies that merged. One was known for agility and rapid development cycles; the other emphasised structure and thoroughness. Rather than identifying how to integrate product development in a way that leveraged both speed and reliability, leaders became drawn into debates about processes, reporting structures and norms. 

Eventually, coordination broke down, and the integration ultimately failed. This pattern is surprisingly common. Organisations tend to choose one set of practices over another, often reflecting the preferences of the acquiring firm but neglecting valuable capabilities.

Research on intergroup conflict and post-merger identification suggests a different approach: Groups can orient towards a shared objective without feeling that their distinctive strengths must be eliminated. In this context, a clearly defined purpose plays a critical role.

Purpose doesn’t remove differences, but it helps organisations distinguish between what’s consequential and what’s not. It provides a basis for deciding where alignment is essential and where practices can diverge. Because this question was never resolved by the two software companies, attention drifted towards more visible but lower-stakes issues while the deeper integration challenge remained unaddressed.

Our recommendation: Be clear on purpose but flexible on execution. Define a small set of non-negotiable principles or objectives and be flexible about how to achieve them. This preserves valuable capabilities while maintaining strategic coherence.

What effective cultural integration looks like in practice

When Microsoft acquired code-sharing platform GitHub in 2018, the two companies brought very different cultures to the table. Microsoft emphasised enterprise scale and operational efficiency, while GitHub was known for its developer-centric and informal culture.

At the same time, both organisations were aligned around a shared principle of empowerment. GitHub’s mission to help developers was fully aligned with Microsoft’s mission “to empower every person and every organisation on the planet to achieve more”.

Rather than forcing convergence, Microsoft preserved GitHub’s developer-first ethos and gave the company a significant degree of operational autonomy. For example, GitHub was allowed to release new tools that enabled developers to deploy code directly to Amazon Web Services, Microsoft’s biggest rival in the cloud market. By preserving GitHub’s unique way of working while aligning on a shared purpose, Microsoft was able to maintain what made GitHub distinctive without sacrificing strategic coherence.

The strategy paid off. In 2018, before the merger, GitHub had 28 million active users and annual recurring revenue (ARR) of some US$250 million. By 2022, the company had tripled its user base and crossed US$1 billion in ARR.

From ancient history to modern M&A, the challenges of cultural integration remain consistent. Successful cultural integration of two entities doesn’t mean eradicating differences. It’s about clarity of purpose, as well as making disciplined choices about what must be aligned, what can remain local and how those choices will be understood by employees. 

Leaders who approach integration in this way don’t topple “local gods” – they channel them in service of a shared vision.