2 issues I want to address:
Your Civics:
-Free Speech does you little good in this situation. You're already planning to dominate and want to start your conquest of the 2nd continent, the culture bonus is meaningless and the +2
is nice, but tech and money is no longer your goal, you need units. Free speech is good to go for a cultural victory or space race from here, but for war, you want
Nationhood so you can draft units from cities with excess happiness.
-Representation is ok up until the big preparation for war, but once you decide to go all in,
Universal Suffrage is even better than Police State. You can set your
to 0%, rake in the cash, and hurry tank/infantry production in each city to produce an enormous army and easily wipe out the other continent.
Your Tech Choices:
You probably should have had Military Tradition a long time ago, Cavalry and Cuirassiers can be accessed earlier than most units that are able to compete with them and could have helped dominate your game much earlier! (I'm in an immortal game atm where I had Cuirs at 1200 AD and Cavalry at 1430 AD, timing helps a lot!) I would have skipped some of the techs like Communism, Biology, Scientific Method, and Military Science. They are great techs, but not for the timing you chose to kill the other continent. Instead of them I would go for Assembly Line -> Industrialism, you could already have 20
Infantry invading instead of the 14
Riflemen, and have Industrialism 1/2 done for tanks! (Assuming nobody would have/trade you Steam power, otherwise industrialism could be done!)
In your current situation, you have 3 good options:
-It could be possible to get away with an immediate switch to Nationhood (keep representation to help tech for a bit.) and drafting plenty more riflemen. In 10 turns your Riflemen count could rise from 35 to near 80. The entire continent could declare war on you and it wouldn't matter.
In this situation, it's your call on if you still declare on Alex immediately or not for a few turns.
-Abandon the idea of war until you have Assembly Line and/or Industrialism so you can fight with a much larger AND stronger army than any of them will be capable of at the time, if you want to do that war, do 0%
after Assembly line or Industrialism and upgrade all your riflemen to Infantry before buying new units with Universal Suffrage.
-Abandon the idea of war permanently and secure the Space Race.
As for
who to hit, Alex if fighting very soon, Korea if taking a minute. Target the city of Washington (Apostolic Palace + The Great Lighthouse) and Seoul (The Kremlin). These wonders will help a great amount.