Initial blueprint of the Tsar bomba had a target of 100 MT device, scaled down to 50 MT for the actual bomb detonated in 1961.
A 1 Gigaton bomb would have been 10/20-time more powerful than the Tsar bomba, not 1000.
This is hardly a extinction-level device in my opinion: for reference the...
As it was said above, in OTL the referendum between monarchy and republic was a close call.
So it is entirely possible that even few different decisions could have been resulted in a preserved Kingdom of Italy.
For example, King Vittorio Emanuele III decided to flee Rome between 8 and 9...
The political attributes of the title of roman rules changed steadily over time (just like the overall state organization below them), but if we really want to pick a specific date for the end of the dominate, I would choose March 21st 629, when Latin titles were dropped in a law and the term...
I'm a little puzzled by the thread title: in fact, as far as i know, Romans DID conquered Germania magna in OTL and hold it for a generation... ;)
The conquest began with the campaings of Drusus Germanicus (Tiberius' younger brother) in 12-9 BC and continued with the campaign of Tiberius in 4-5...