Continuing past 1 AD, my goal was to build cannons before beginning a war of conquest. Caravels let me meet the rest of the AI and get the circumnavigation bonus. Ragnar and Shaka were at war when I met them, but they'd later become best friends.
I researched Steel in 1330 and attacked Monty in1350. I captured four of his cities, including his capital, when he capitulated in 1460.
In 1480, I attacked De Gaulle. Shortly after that, Ragnar and Shaka attacked Wang Kon. Their war went nowhere, but I took three French cities and accepted De Gaulle's capitulation in 1535.
I researched Rifling (which Ragnar already had) in 1555 and started upgrading my units. He and WK made peace in 1575, but since Ragnar still didn't have cannons, I decided to press on and attack Ragnar in 1600, without having scouted out his forces. Big mistake! I captured Oslo, but his massive reserves of cavalry and riflemen recaptured it and wiped out my invasion force (including the starting longbow, which had been upgraded with a GG). When he called an AP vote to stop the war in 1615, I didn't resist.
Discouraged, I took a week off from the game and watched another of Lain's deity-level games for inspiration.
When I came back to the game, I decided to concentrate on my economy and science (with some help from my vassals), aiming to have tanks before I resumed the war. I used one GE to found Mining, Inc. and another GE to speed the completion of the Pentagon.
Ragnar and Shaka attacked WK again in 1720. Pyongyang fell quickly, followed by Seoul. I had finished researching Industrialism, and although I hadn't built all the tanks I wanted, I knew WK wouldn't last much longer, so I landed the forces I had in Korean territory and declared war on Ragnar in 1800. At first, it was a defensive war, but as more of my reinforcements arrived, I captured Seoul and Pyongyang, then pushed into Viking territory. Finally, I captured Nidaros in 1860 and Ragnar capitulated.
Now, having saved Korea, it was time to make it my own.

I attacked in 1862, captured two cities, and WK bent the knee in 1870. Meanwhile, Mansa Musa (who had one city reaching legendary status and and one component of his spaceship completed) finally ended his neutrality and attacked Shaka. Although they fought naval actions, I never saw any amphibious invasion.
Back in 1812, I had been elected Secretary General of the UN, having had exactly enough votes from my vassals to win that position. Another UN vote came up in 1872, and now I had more than enough votes to win a Diplomatic Victory, but this year was time for re-election as Sec. Gen. So...on with my wars of conquest!
I attacked Shaka, captured four cities, and accepted his capitulation in 1882. I immediately declared on Mansa Musa.
Another UN vote opportunity arrived in 1884, but I was close enough to my goal of conquest that I declined to call the vote. I only had to take two of MM's cities before he capitulated, giving me a Conquest victory in 1892.
So...I figure that my mistake in the First Viking War cost me at least a century, and I'm sure someone else will have met this goal much earlier. Still, this was pretty much a legitimate Immortal level game (the longbow helped in the early game with the barbs, but didn't play any significant role against the AI) and I'm pleased with my victory. After a decade stuck in a rut of Monarch-level play, I think I'm finally upping my game!