What exactly is a merge conflict?

Solution 1:

You will have a conflict if you merge:

• branch2 to master (no conflict)
• branch3 to master (conflict):

That is because:

• The common ancestor would be master (with a second line empty)
• the source content is branch3 (with a second line including "3")
• the destination content is on latest of master (with a second line including "2", from the merge of branch2 to master)

Git will ask you to choose which content to keep ("3", "2", or both).

First, do the merges after:

git config merge.conflictstyle diff3

See "Fix merge conflicts in Git?".

Solution 2:

A merge conflict happens when two branches both modify the same region of a file and are subsequently merged. Git can't know which of the changes to keep, and thus needs human intervention to resolve the conflict.

In this case, your steps 2 and 3 create two branches that have conflicting changes.