First choose Germany as the nation you are going to play with.

Before you do anything start saving up your political power and once you have enough justify on Ireland to annex them. Since you are Germany it should be easy enough and since it's the start of the game no one will try and stop you.

After that you have two options. The quick one is to just justify and declare war on Czechoslovakia to get the achievement easily (Note:You still have to do the "Oppose Hitler" focus and get the "Our Place in The Sun" focus to get the achievement).
However, if you don't want to wage war do the "Oppose Hitler" focus and form the German Empire. It doesn't matter if the Dutch give you the Kaiser back or not, just go down to the "Rekindle Imperial Sentiment" focus then wait for Austria-Hungary to form and just prepare the Italian coup and get the "Monarchy is Back in Fashion" achievement while waiting for that to happen.

Once Austria-Hungary reforms it should join your faction that was created when you were going down the focus tree to complete the "Rekindle Imperial Sentiment" focus. Allowing you to get the achievement.