You have done multiple mistakes. I hope you did not erase your previous saves because I have a feeling it might be better to reload from a significantly earlier time. Still, the position is not lost and it may very well be salvageable.
Problem number 1: You have no Wonders. Technically, this should be a good thing, but you don't have much in the way of troops or city suport either, so one wonders what you've been doing all this time.
Problem number 2: Your workers are working on the wrong tiles. You have a significantly lower number of workers than I would personally be hosting myself and at least 2 of them I saw were on automated action. Never automate your workers. I only automate workers to clear pollution and sometimes not even then. Your core cities have multiple underdeveloped and overdeveloped tiles. This means that you have wasted enormous amounts of worker turns. You should only improve what you want to be using, no more, and certainly no less. You have at least 6 Workers doing pointless jobs. Two are working on roads for far flung and small cities, one is mining a hill that won't be seeing use for a long time. Even if it does, its use will be situational, as the corruption in that city is liable to eat up the extra shields.
Problem number 3: Your cities are working on the wrong projects. Knights Templar is a serious mistake, as you will soon find out. The Americans have beaten you to it. This should not come as a surprise. You should have been keeping tab on prebuilds and straight builds on the F7 screen. Moreover, one city is working on a library which will not boost commerce at all, probably for at least another 500 years, and multiple cities are working on marketplaces when you neither have the population to support it or the luxuries to justify it. Make more Courthouses, create the Forbidden Palace, make more military units.
Problem number 4: You know nothing. You don't have embassies anywhere and large swaths of the map are black. Arrange an RoP with the Incans and explore their territory prior to making any rash decisions. They are more powerful than you, Pikemen be damned. If they're as big as I suspect they are, better units will not save your bacon. You'll be dead meat if you war with them.
Problem number 5: You have no luxuries. As much as 25% of your core city productivity is lost because of unhappiness. That's majorly huge. You should have seen this coming and a) secured more luxuries and trading routes or b) built more cathedrals and colesseums where they're needed. I daresay it would have been better if you had built a Cathedral and a couple units in Trondheim rather than the now wasted KT attempt. As much as possible, never build Wonders in your capital. Building Wonders in the Capital deprives you of at least 2 prebuild preservation options should your attempt be thwarted: 1 Palace, and 2 Forbidden Palace.
Problem number 5: Your units are badly placed and badly proportioned. All MIs? Firstly, you'll need more than this, and secondly, you'll probably need bombarding equipment. You have a good MI base and Chivalry, so that's something, at least. Make peace with the Incans and trade for Theology. That way, you can funnel the foiled KT attempt into a Sistine Chapel. Don't sit on that, however. Find the city that's building the rival Sistine Chapel and Investigate at once. If you can't make it, abandon the attempt in favor of a Cathedral. Position your troops closer to key invasion points, preferably in good, defensible positions.
You have 2?!?! Galleys!!!
You're Viking! Your kingdom should have at least one Galley to a city. What the heck are you going to do with your Berserks if you ever muster enough resources to build some? Send them over on foot? Build more Galleys.
All in all, it's a pretty messed up situation. I'd build a few Galleys, reposition the Workers, work on the happiness issue and war with the Aztecs. That's right, the Aztecs. The Incans are an unknown and unquantifiable force. There' no way a war with them is advisable. The Aztecs are fortified, but they're small and probably not too numerous. You can take them on with Catapult enhanced stacks and later, Trebuchets. The obvious angle here is Dyes and Wines. The Aztecs have both on their land and your civ can use these resources very, very much. The additional control over the Iron resource doesn't hurt, either. With luck, you'll be able to finish the war with the Aztecs before Cavalry come along and you'll be able to maintain a stranglehold on the Iron trade.
The Russians, I suspect, are sharing part of the blackened space with the Inca. How much, we don't know, but probably a significant amount, since the Inca aren't really that far ahead of you. Obliterate every piece of black space you can find. Don't send Workers. Arrange RoPs and send Horsemen.
I fully agree on a war with the Aztecs, but you should probably set your house in order first.
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