HOW did Pharaoh Narmer (or Menes) unify Upper and Lower Egypt? (Ancient Egypt)?

Did he achieve it through military force?
Did he achieve it through a more peaceful means?
Or neither. HOW exactly did Pharaoh Narmer (or Menes) unify Upper and Lower Egypt.

Refer to the Narmer Palette - if needed.
Please show your source.

Thank you.
6 answers