Berlin, Munich and what other place in Europe?

I'd suggest playing around with the train schedules (and fares) on the Deutsche Bahn website. In Berlin and Munich you will be closer to Poland, Czechia and Austria than to France, but the travel time (and perhaps cost) are more important than the actual mileage. Try to select the correct day of the week for you departure from Berlin (if you know it), since schedules can vary.

I would spend at least a couple of days in a small town - more chance that he can speak German with those that don’t speak English

You might want to consider stopping by Dresden on the way to Prague. It's a straight shot on the train.

I agree with everyone who has posted, which is a problem because they have all suggested different things.

My initial reaction was to say skip another country and spend your time in Germany. You've got ten days, since your last is spent flying out and your first you'll be experiencing jet lag. You don't say how long you plan to stay in Berlin, but I would suggest four nights (3/24-28), as that will give you three full days plus your arrival day. Are you interested in doing a day trip to Potsdam? The program I was on took us there, and Frederick the Great's palace - Sanssouci - is well-worth it, especially if your son is interested in that period of history (is there a period in which he's especially interested?). It's a very easy 2-3.5 hour (depending on stops; some are direct) train to Dresden, which I absolutely think you should see. It's a beautiful baroque city, and the rebuilt Frauenkirche ties that period to the Second World War. If he is interested in places switching countries, you can take a days rip to Goerlitz, which was cut in half post-WWII when the German-Polish border was moved west. You can walk across a bridge to the Polish side. Full disclosure - I visited when the town was still included in the Rick Steves guidebook (it apparently no longer is) and my friends and I still couldn't find the damn bridge, and the brewery I had emailed confirming our visit was closed and shut tight. BUT I know others around here have crossed the bridge, so if you decide to visit you will have plenty of people to help give you directions. Bridge or no bridge, it was still a fun visit. After Dresden you could see Leipzig, Weimar or Nuremberg on your way to Munich, although probably not all three. I'd aim to get to Munich by April 1, which would give you two full days and most of a third. Are you planning on seeing Dachau? Neuschwanstein? If yes, then maybe arrive by the 31st?

If you do want to add another country, then Prague is the best bet. You could even stop in Dresden for a few hours on your way from Berlin to Prague - although I really urge you to spend at least one night in Dresden. You could do four nights Berlin, four/ three nights Prague, four/three nights Munich. I will throw out Wroclaw, Poland, which was Breslau, Germany, until the end of WWII. So it's a cool mix of German, Polish, and regional Silesian. BUT it will take you five hours from Berlin, about that the Dresden, and 12 hours to Munich. It looks like Lufthansa flies from there to Munich, but I have no idea the timing or prices.

It sounds like it will be a great trip, whatever you decide, and your son sounds like an amazing young man. Please do let me know if there's a specific period or topic he's especially interested in; I can send you some books I would assign for class, if he'd/you'd like.

I've been to Görlitz twice and can confirm that the bridge exists. In fact, last year I stayed on the Polish side (Zgorzelec) because a ceramic fair drove up rates on the German side. The German side is prettier (partly because a lot more money has been available for restoration, some of it from an anonymous donor), but there are some very attractive buildings on the Polish side as well--not necessarily evident before you cross the bridge and walk a little way toward the center of that part of town.

Görlitz is one of the loveliest towns I've ever seen, with a variety of architectural periods represented. It's rather obscure location keeps the number of tourists at a reasonable level, at least most of the time.

I'd look at a map and decide which other country makes the most sense to visit in your travel plans. France, Poland, Czech Republic, or the Netherlands?

Strasbourg would be my pick though because of the borders going back and forth so many times and it is a beautiful city. Travel from there to Munich isn't that long of a train ride either.

In Berlin, try and visit Sachsenhausen as well as Ravensbruck Concentration Camps. They offer 2 different perspectives about which groups of people were persecuted.

If your son is a history buff there are not many options where the big nations of the last centuries played in Europe: Berlin (you have), Paris, London, Vienna, St. Petersburg. Also other nations at start but less powerful and influencing - which says nothing about cultural relevance and beauty on their own. Prague and Amsterdam are nice and also have historic relevance but were not the big players.

Two options.
- Paris after Berlin (flight) and by train via Alsace-Lorraine back to Munich
- Vienna after Berlin, e.g. by night train (NightJet)

Plan 5-6 full days for Berlin which is so full of history in multiple layers and other interesting attractions. In Berlin do a longer guided walking tour through eastern center and visit German Historic Museum. My city has a lot of French imprints. Around 1700 20-30 % of people living in Berlin were French. One of our most beautiful places on the city still has a French name: Gendarmenmarkt. Our presidential palace has the name Bellevue. Also local food Bulette has a French origin.

Newest tip for Berlin history buffs: a few days ago the new app "berlinHistory" was launched with a lot of interesting information. They worked closely with local institutions.

If your son is interested I am open to share some insights and views.

We are starting in Berlin on March 24 and will end up in Munich
before going back home to California on April 4, but I'd like to stop
in another country close by in between.

10 days on the ground? Most people recommend 5 days in Berlin, with a day trip to Potsdam, and 4-5 days in Munich, with a day trip to "the castles", as Americans call them, or maybe Dachau or Salzburg. Salzburg is in Austria btw., so this would your second country.
What I want to say: you don't have the time for detours to other countries. Prague for example deserves at least 2 days, better 3, and each time you move from one city to the next you lose at least 1/2 day.
In your case I would recommend a day trip from Berlin to Poznan ( 2 1/2 hours), which is a preserved and pleasant city in Poland with several very interesting sights and a rich history.

Thank you so much for all the insights and wonderful suggestions - especially how much time we should plan for each city; that is really helpful. I have learned so much reading these responses. I will look at Görlitz which sounds great and I wasn't considering that before. I think we'll skip Neuschwanstein on this trip...it will take too long. I'll follow-up with what we decide to do and see. Thanks again!

Strasbourg is a good choice, but other than that you son's interest in history offers a ton of places, a ton of choices which he could track down and see, be it in Germany, Poland, Czech Rep , Alsace-Lorraine, or elsewhere in France, Belgium. Keep in mind Germany is bordered by 9 countries.

"He is obsessed with it." Fantastic...a history fanatic. Does he want to focus on German sites...cultural sites and museums, musical, war, battlefield sites and memorials, military museums, the Prussian monarchy, Prussian historical sites, WW1 , WW2,, etc.

Since he is fluent in German...fantastic...he has a lot of choices since doesn't have to use audio phones or depend on English translations/explanations, he's able to read the German in artifacts, ie posters, newspaper headlines, placards, or at historical cemetery eulogies, quotations in museums with no English,...all helps to get much more out of what you're seeing.

Between Berlin and Munich...again numerous historical sites, depends on his historical priorities and depth of interest.

I would stick with places closer to Berlin and Munich to minimize travel. Dresden, Prague, Regensburg, Nuremberg and Augsburg are great places to visit in that general area.

Hi,

How far are you willing to deviate going from Berlin to Munich in search of historical sites, ie to track down these places?

I would suggest Leipzig, Jena, Lutherstadt Wittenberg, Meissen, Hannover, Weimar, Naumburg an der Saale, Celle, Lüneburg, Potsdam, Munster/Örtze, Ingolstadt, Ulm, Minden, Hameln,