I am dealing with a similar situation; previous teams merged into one with subsequent respecifying of roles and grades. Some legacy political forces were in play.
As the Scrum Master you are the master-servant of the team including coaching. Many agile commentators forget the master part but the business is paying you to impose your will upon the team to make them a productive, cohesive unit. You are not a tea-boy. Reaffirm to yourself that you are in control of team.
In the immediate instance I took the following actions
Commitment to the Team
Sit the entire team down including the warring developers and tell them that from now on the team will finish all discussions with the following mantra
- Agree and commit
- Disagree and commit
Either way, the meeting will close with a commitment to the team that an approach will be used and each developer will do their utmost to see the course of action succeed.
Non-commitment will not be tolerated.
When Developer A and B next decide to engage in a lengthy debate about a particular aspect simply tell them that the matter is decided and as a team we (IE you) now expect commitment.
I know some individuals on this forum may take issue with treating developers with such a hard line but in my experience not all team members respond to gentle encouragement to adopt a team spirit. People love change but some hate being changed.
In the longer term you could invest time in
5 Dysfunctions of a Team
The 5 DOAT is a fairly popular framework for producing high-functioning teams. Each dysfunction is, coincidentally, mirrored by the 5 Scrum Values of
The 5D book is a very short read and a number of different workshops and team building events can be organised around the themes. I have attended two Workshops whereby we implemented the 5D and in each time the team emerged stronger, with more empathy and with a higher output.
To illustrate the differences in the team considering using the personal timeline tool.
Each team member draws up a personal timeline of high points and low points across a horizontal axis of time. It can be as detailed, colourful or personal as you like it.
It requires high levels of courage to be the first presentation which is why the Scrum Master should go first.
In our sessions normally half the team end up crying as people tell the stories of their life that led them to the current team.
Stories of family deaths, heroic war actions, divorces, bankruptcies, abusive husbands followed by educational attainment, spiritual fulfilment, marriages.
The personal timeline over a couple of bottles of wine and pizza was the best team building exercise we ever did to understand everyone's motivations and empathise with them. You will learn which developers fear being a bad father allowing you to prioritise their children's events, which developers were high achievers (harness their ambition), which team members suffered a life-event which impacted their productivity etc...
It may be that Developer A and B both list joining the new team as a low point and by offloading that vital information to the team you see an immediate improvement.
In short you build a tribe that has an inherent loyalty to itself.
Lastly, consider letting one of the developers go.
It does the following
- Reaffirms who is in control during the forming stage. You.
- Solves the issue
- Sends a strong message to the team that you expect team loyalty and productivity
- Will not tolerate negativity for the sake of old allegiances, it is a new day.
I personally do not believe that any new scrum team survives first contact with the process without losing an individual who refuses to accept the new status quo.
I should also add that my approach, focussing more on the master part, has worked extremely well. We had to let one developer go (the team had lost all confidence in him) but everyone else has gelled and adopted a Scrum mindset.
We have month-long sprints with Planning sessions have decreased from 18 hours in total to lasting less than 6 hours (due to disagree and commit) and our stand-ups went from 41 minutes to 23 minutes on average.
In addition, senior management were happy that the team were under the Scrum Master control rather than a runaway train they were previous. The Product Owner is much happier that the Scrum Master is willing to lead when required and allow Agile principles to guide wherever possible. I am writing a white paper on our experience at present.
For those horrified at my strong line I should also add I took a similarly strong attitude to management, streamlining the amount of meetings, updates and reports the team were scheduled to attend.
I can already envisage a time when I leave the role as I feel the team will be a completely self-managing unit who no longer require a Scrum Master.
Edit in 2021
This answer, whilst highly upvoted, is the answer of a junior Scrum Master on an Agile journey. There is a considerable amount of advice in this answer that I do not agree with any longer and have matured beyond.
The language is unnaturally combative (I had recently left the Armed Forces) and shows a strong misunderstanding of Servant Leadership, even going so far as to use the word Master. It refers to imposing will upon a team which is absolutely not the role of a Project Manager, Delivery Manager, Scrum Master or other equivalent.
Learning to use influence is a sign of business maturity and reflected in the Agile Manifesto.
I have left this answer on Stack Exchange to show that everyone is learning and evolving and we draw upon our experiences. I would not approach a feature team with this attitude any longer and would seek to find a way of working together wherever possible.
However the references and the concept of Disagree and Commit are still strongly encouraged for all.