Aztecs

The Mexica or the Aztecs, as they are popularly known, are an agglomeration of ethnic groups that formed the largest empire in Mesoamerica, known as Ēxcān Tlahtōlōyān, or Triple Alliance, at its core consisting of the allied city-states of Texcoco, Tlacopan, and Mexico-Tenochtitlan, and centered on the latter. The city of Tenochtitlan, de facto capital city of the Empire and one of the world's largest cities over the course of its history, was a finely planned metropolis built over Mexicoh Island, on the once great lake Texcoco, the place of today's Mexico City. The empire spanned the entire Mexican Central Plateau, also known as the Mexican High Plain, and even today the extent of their influence can still be felt in the entire region, permeating many aspects of modern culture, specially in central Mexico.

In-game, they are the equivalent of the Mongols to Western Europe, arriving in the 1350s with a large fleet and a massive army to conquer the known world. With it comes diseases, conversions and conquest of the Western World. As a Catholic/Muslim state, you must take out these invaders, no matter what the cost. They can be encountered if patch 1.09 is installed and the Sunset Invasion expansion is installed.

In the "The Old Gods" DLC, it is revealed that the Aztecs gained their knowledge of shipbuilding after a chance encounter with famed Icelandic explorer Thorfinn Karlsefni ended in most of the Vikings being slaughtered and the Aztecs taking their longboats back to Cemanahuac. 

Really, a Threat from the West? Across the Ocean?

To encounter them, first, you must choose a kingdom with access to the Atlantic Ocean which are of the following as of 1337:

• Kingdom of England
• Kingdom of Wales
• Kingdom of Scotland
• Kingdom of Norway
• Kingdom of Sweden
• Kingdom of Denmark
• Kingdom of France
• Kingdom of Portugal/Galicia
• Kingdom of Navarra
• Kingdom of Castille & Leon
• Marinid Sultanate of Mauretania

In the 1340s after the game begun for at least 3 years, a warning will be given to the player, whichever nation he/she rules, about a menace from the West, with a great emperor of the Aztecs with a threat of an invasion. However, a more direct warning will be given to the player if he/she is a ruler of the kingdoms said above. Then after 10 years or so there will be another warning about the Aztecs, which is more real than ever.

Wait, They're not Kidding here....

The Aztecs have come, and with a massive army because Europe rejected them of land. First, a message will appear to the player about a massive fleet approaching and armies never seen in the world with demonic gods and the people cowering in fear. Then the official announcement of the invasion of the player's kingdom follows. 

Then, you can see the full extent of the might of the Aztec army: 1000 ships alone in a mighty fleet, 80,000 to 120,000 men combined into 4-6 different armies with 20,000 men each, all infantry and archers with no cavalry whatsoever. Any county that the Aztecs land into instantly convert to their culture and religion: being Nahua and Aztec respectively. 

Usually, the nation invaded by this scourge will fall rather quickly because of the lack of troops to fight the Aztecs, and their title taken from them, becoming dukes instead of kings. Much like the Mongols, the counties taken will become the Aztec Emperor's direct holding in the Old World, with a twist.

When they take over a county, any courtiers/leaders is subject to be sacrificed by the Aztecs to please their gods. This situation can put the player to a difficult situation if a family member is taken to be sacrificed to the Aztec gods.

However, that is not all. The player will receive a second message of another Aztec invasion in a different kingdom with, usually a smaller army but still eminently massive enough to conquer whichever kingdom quickly and without mercy, and as usual, courtiers will be taken and sacrificed, and the county which they land in instantly converts to their culture and religion.

How do the rest of us fight them?

Here's a usual scenario of what happens when the Aztecs arrive: Portugal usually became the first nation conquered and the Marinids second. After that, they will expand to the rest of North Africa and the Iberian Peninsula, with it comes down the Kingdoms of Castille and Leon, the Nasrid Emirate of Granada, and the Kingdom of Aragon and Navarra, while in North Africa, the Zayanid Emirate of Alger comes down second with the Hafsids of Africa falling next. 

However, after the conquest of said nations, their armies will run out of steam and have to rely on standard levies and retinues after they arrive to French Aquitaine and Bahri Egypt. With the conquered subjects, there are usually many rebellions from both Catholic and Sunni vassals, and this is where the players, who are not invaded yet can use their advantage on the Aztecs.

Based on the said scenario and with the rebelling vassals, 3-4 nations can act against this new scourge being: the Bahri Sultanate of Egypt, the Sultanate of Mali, the Kingdom of England and the Kingdom of France; or if France/Norway held Iceland is attacked first, then Sweden and the Holy Roman Empire can act against them. These are the reasons why:

• The Bahris, being the most powerful Sunni Muslim state, and the possible target next, can raise up to 120,000 troops from levies and some 30,000 troops from retinues if possible, but they have an ace card: the Mamluks. The Mamluks, loyal guards to the Sultan, is a raisable mercenary force that is a vassal of Egypt, similar to the Ghilmans of the Seljuks and the Varangians of the Byzantines. The Mamluks are 23,000 strong by 1337, so essentially they are an army of their own, so the Sultan can push back the Aztecs with these troops.
• The Sultanate of Mali, being inland, is more likely safer from the lurches of the Aztecs, but since they number far fewer than the Bahris, with a maximum of 30,000, they can hope for rebelling vassals or when Egypt declare war, and that is when they should act, for all of the Aztec force will be stuck fighting, then the Malians can strike unknown, and they can win despite their smaller numbers.
• England, an island nation, with full access to the seas, and therefore many ports, have more fleet levies than most nations, and since their levies are smaller than most European nations, with a maximum of 80,000, while the rest of Europe can raise 100,000, they cover that with their archers being more powerful when attacking, with a standard 60% attack increase from normal levy archers, because they use English longbows. With that combined with a powerful army of at least 70,000, they can inflict more damage to the Aztecs and can defeat them nonetheless.
• France, a massive nation second to the Holy Roman Empire and tied with Sweden in area size and levy amount, has a lot of ground and therefore a massive levy and retinue that can be assembled, with at least 150,000 troops, but a distinct advantage that they get from their armies is their powerful cavalry force. French cavalry can gain a 45% attack increase and some more from the stables upgrade of a barony, giving their cavalries a massive crushing blow when fighting the Aztecs, and since the Aztecs barely have any cavalry and little to no pikemen, the knights of France can crush them in battle if 100,000 Aztecs fight against 100,000 French. 
• Sweden, also a massive nation tied with France, have a lot of ground and this gives them more time to prepare since moving from a territory to another can take as long as two months, with the tundras that cover the territories of Sweden. An advantage that they have is their infantry that has a standard 45% attack increase, therefore, the Aztec infantry can be defeated by Swedish Huskarls in an equal fight. 
• The Holy Roman Empire, being the most powerful Catholic state in Europe, has a massive advantage in numbers, since the levies can go up to at least 200,000 with good vassal relations. Also, they have the same advantage in their knights and cavalries with a 45% attack increase, with the French, so their knights can defeat the Aztecs in an equal fight.
• Denmark, although this can be really hard on some inexperienced players. Denmark is not big like the other countries and they lack the levies to defeat the Aztecs directly, with a maximum of 30,000-50,000 troops against 120,000 Aztecs. However, with the right use of marriages and therefore alliances, they can ally themselves with stronger nations like Sweden, France or the Holy Roman Empire to repel them. The Danes also have a similar advantage on their heavy infantry with the Swedes, with a 45% attack increase, and since they are between two of Europe's largest nations, Sweden and the Holy Roman Empire, they can use them to their advantage. Also, if they can subdue the Teutonic Order by vassalization, they can increase their numbers significantly with levies and the Order's troops.

These are a number of nations that can defeat the Aztecs, but with considerable micro-managing, casualties can be kept lower and the Aztecs can be defeated with lesser amount of men. Also, since the new feature of offering to join wars, then most rulers with a similar religion can offer assistances to those being attacked by the Aztecs. However, Catholics have a greater edge that is similar to the Bahris but not as numerous: Crusader Knight Orders.  

If the game is played pre-1317, then there are 3 Holy Orders that can give assistance to the players who played as a Catholic, namely, the Knights Templar, the Knights Hospitalier and the Teutonic Order, and each has a maximum force of 7,700 men, combined they have 23,100 troops at maximum, similar to the Mamluks. However at 1337, there are only 2 available since the Templar are exterminated, so only the other two has the service available.

What Happens Then?

If the Aztecs are defeated by said nations, they will recede their territories due to the war and if full wars are managed, then the Aztec can be set back to a few small holdings and their defeat will be inevitable.

Once they are out of Europe with no holdings whatsoever, then a message will be given saying that their armies return to their origins and there will be a reprisal from Europe, who will come to their shores and give to the Aztecs what they did, with interest.

If you managed to win against the Aztecs, then congratulations, you can defeat any other nations since you proved to defeat the most powerful invasion that Europe has ever seen since the Mongols in the East in the 1200's and the Muslims from the Middle East in the late 600's and early 700's.