what were the three reichs
The Second Reich was Imperial Germany (1871-1918),  as unified by Bismarck in 1871.   Note. During the Weimar period (1919-33) the official name of  Germany was still Deutsches Reich..    ________     Hitler's regime was never officially known as the Third  Reich. The term was first discussed in 1923 by German historian  Arthur Moeller van den Bruck in his Book Das dritte Reich  (The Third Empire), which he hoped would soon come into beling.
Hitler referred to Germany under his regime as the Third Reich. He wanted to create a new government that would rule Europe for 1000 years.  The Axis was the alliance of 3 countries, Germany, Italy and Japan, that fought against the Allies. Other countries also joined or were forced to join the Axis.
The First Reich was the Holy Roman Empire. There is little agreement as to when it was founded. Most German historians date the foundation from the coronation of Otto I in 962. That 'empire' had a continuous existence till 1806. The Second Reich was created by Bismarck in 1871 and lasted till 1918.