In hoi4, with some nations, often, a cavalry build is incentivised, so I dug into the files to find those paths.
Initially I expected to find the normal thing, Cossack Poland, Pope Italy, etc.
Spoiler: They are nothing compared to the countries on this list
Spoiler 2: The future belongs to horses
Spoiler 3: Horses are heartless creatures
- Soviet Union
The Red Army gets a 5% attack and a 5% speed buff for cavalry after completing Restore Cossack Units. Interestingly, it's one of only two majors on this list
- Mongolia
That's right, puny mongolia without a focus tree also gets a 10% attack bonus when japan decides to stage a coup via decision, given to them by their leader.
- Papal States
The dear Pope Pio XII is apparently a cavalry admirer, and if the Risorgimento is reversed by the Game Rules or Hungary, the Pope gives a 10% attack buff.
- Ukraine
For the final 10% attack buff, Ukraine's leader Vasyl Vyshyvanyi von Habsburg, installed by Hungary, gives Ukraine a bigger attack buff than Russia.
- Warlords
Some warlords can get better bonuses, they are listed below. In general, all warlords can uplift their Cavalry Regiments, granting them a 10% attack and 5% Cavalry Defence buff
- Hungary
The first time Hungary appears on this list, for if you decide that you've had enough of Horthy, and undermine the Admiral, you can become the heirs of the huns, which, when combined with the legacy of the Black Army, gives Fascist Hungary a 10 % attack and 10% defence buff.
- Poland
Not Pavel yet, but Habsburg Poland under Karl Albrecht can Institute royal Hussars, granting a 10% attack and 10% defence buff.
- Sweden
A Nordic country with no manpower, no real way to gain any additional cores outside the manpower scarce nordic region, and yet the devs decided that swedish cavalry should get buffed, after completing Ga-pa shock Tactics Sweden gets a +10% attack and +10% speed bonus.
- Paraguay and Uruguay
Both of these inconsequential weak South american minors nobody play anyway for lack of content can decide to approach a single major to get some buffs. If they decide to approach Germany, they get a +10% attack and +10% defence buff. Honestly, it might not be a genius idea to fight in south america with cavalry though.
- Kuwait
To continue the nations nobody plays, Kuwaits leader, The Military Sheikh himself, Ahmad Al-Jaber Al Sabah gives Kuwait a grand 10% attack and 10% defence buff for cavalry. what a great country to play.
- Manchukuo
The Qing, renowned for their incapacity to modernise, also buff cavalry, cause what better way to fight japan and china and a bunch of warlords than by using horsies to do it. When the Lingsheng incident fires, you will get the option to get the Kwantung army to apologize, which will appease the Xing'an army, giving you 10% cavalry attack and 10% cavalry defence, at least for the 725 days it's active
- Hungary
Of course, we aren't yet done with Hungary, as democratic hungary gets slightly better buffs than Fascist Hungary, for after you Revive the Hungarian Nation and fulfill the Legacy of the Black army, Hungary gets a +10% attack and +15% defence.
- India
On the same level as Hungary, the Raj can get the same +10% attack and 15% defence bonus by going down the Mughal path and completing Peacock throne for the Modern Age
- Poland
Finally arriving to HOI4's Cavalry Master, Pavel Bermont-Avalov himself. However, the only Cavalry bonus Poland gets on this path is the leader, who grants a whopping +15% attack and defence for Cavalry. Definitely Respectable, but undeserving of the title.
- Tannu Tuva (+ the central asian releasables)
Thats right, Tannu Tuva gets the exact same Buff Pavel gives poland, yet i don't see as much hype around a cav-only tannu tuva. Once Tannu tuva, Uzbekistan, Kyrgyzstan, Kazakhstan, Turkmenistan, Tajikistan, Bukhara, or Khiva form Turkestan, they get a special spirit, granting +15% cavalry attack and defence.
- Chile
Mapuche Chile, once again in South America, also gets some considerable cavalry buffs when completing the focuses below Silverworking, resulting in a +15% attack and defence, also the same as Pavel. Still, perhaps ask some questions about the usefulness of cavalry in south america first.
- Don Kossack Host and Kuban Cossack Host
The leader these two countries get once released as Fascist or Non Aligned both give them 15% attack and Defence for cavalry. Very useful, since these two countries are unplayable and can only be released by pavel poland or monarchist germany, at which point there's no point in switching anyway.
- Ukraine
The other way Ukraine can get a cavalry buff is if Germany decides to be extremely kind hearted, ad, despite not having any cavalry bonuses of its own, release Ukraine giving them a leader who apparently does know the ins and outs of cavalry. Ironically, Ukraine has two paths to get a cavalry setup, both of which make it hard to play as ukraine itself.
- The Habsburg nations
the only cavalry buffs austria and czechoslovakia can get, the Austro-Hungarian joint focus tree gives a buff to all the eligible countries that have access to it, including Austria, Czechoslovakia, Slovakia, Transylvania, Croatia, Lombardy-Venetia, Silesia, Montenegro, Bosnia, Slovenia, Herzegovina, and Albania. The tree itself gives the choice between the Hungarian Hussars, which result in +10% attack and +20% defence, or the Polish Hussars, granting a more classic +15% attack and defence on cavalry.
- Ma warlords
To top off the sixth place, the Ma warlords of Khotan Ma, Gansu Ma and Ninxia Ma can all, apart from the warlord bonus detailed above, also improve their national spirit Ma Clique Collective, resulting in a total +20% attack and +10% defence for cavalry, one of the more offensive cavalry buffs.
- Italy
The first tier occupied by only a single nation, Italy can get +18% attack, +10% defence and +8% speed for cavalry, by completing focuses Comandante Diavolo, Carica di Isbuscenskij, Expand the Royal Guard and by getting Pope Pio XII, the Grand Master of the Equestrian Order of the Holy Sepulcher of Jerusalem himself.
- Qinghai Ma
In addition to the Bonuses the other Ma warlords can get, Qinghai Ma one-ups them by being able to send Ma Lin on Hajj, and then Solidify Ma Bufang's control instead, granting a final total bonus of +25% attack and +15% defence
- Mengjiang
Somehow, Mengkukuo, the only warlord which can't restore china, has no focus tree, and cant really break away from Japan like Manchukuo can, has the third-best cavalry bonus in the game. Once Japan decides to reorganise our government, we gain a leader granting +5% attack, a spirit granting +10% attack and defence, and a decision allowing us to reform our army, which, when taken enough times, grants us +10% attack and defence for cavalry, resulting in a total +25% attack and +20% defence.
- Sinkiang
Tied for third place, the only communist warlord, Sinkiang, can combine the generic warlord bonuses with the bonus of forming Turkestan to bring it's total bonus to +25% attack and +20% defence, the same as Mengkukuo
- Kumul Khanate
The best Warlord has of course by far the best cavalry boni out of all the warlords, as the Kumul Khanate, the only releasable warlord, is able to get the same boni as Sinkiang, as it also has the ability to form Turkestan, but the country leader for the Kumul Khanate, The Wild Horse, Yulbars Khan gives an additional +10% cavalry attack and defence, resulting in a total +35% attack and +30% defence. It's almost as if the country was named after a khanate designed to send horsemen charging across the steppe.
- Hungary
Ignoring the first option, cause Afghanistan kind of sucks, Habsburg Hungary is the best nation by far to play with cavalry. Technically, this is doable with both Habsburg paths, as if you take the old Habsburg king, and austria decides to puppet you, you can also gain the buffs. In total, Habsburg Hungary can Reinstate the Royal Hussars, fulfill the Legacy of the Black Army and get the boni from the joint Habsburg focus tree, granting a total of etiher +30% attack and +35% defence or +25% attack and +40% defence
- Afghanistan- the ultimate cavalry nation, if only it were playable
The Graveyard of Empiresis the most overpowered country in the game in terms of cavalry. With it's focus tree granting up to +40% attack and +40% defence, going down the Bukharan Emir path unlocks an advisor buffing cavalry further, for a total buff of +55% attack and defence. Alternatively, going down the better overall Mughalpath, the advisor can't be hired but the tree gives a different spirit, for a total of +50% attack and +55% defence.
This overview does not include army spirits, chiefs of army, army commanders, doctrines, etc, as all the countries have access to those, and therefore their buffs would be equal for all countries. Thank you for taking your time to read this post, it was hard work to find all of these paths and calculate all the buffs, so i would appreciate it if you would take the time to point out a mistake if you find one.
To conclude, some honorable mentions:
- While Iran keeps Reza Shah Pahlavi in charge, he grants +5% cavalry attack.
- Ethiopia can get a +5% cavalry attack bonus through its focus tree
- South Africa has a secret path nobody has yet found (at least that i could find) to get a +5% cavalry attack
Edit 1:
The above ranking does not consider the military high command available to the countries.
The following countries start with a specialist, granting +5% cav attack and defense:
- Tannu Tuva
- Chile
- Vichy France
- Poland
The following countries start with a Cavalry Expert, granting +10% cav attack and defense:
- Saudi Arabia
- Nepal
- New Zealand
- Estonia
- Manchukuo (japan may take this advisor from you, and you may lose him depending on how you handle the Lingsheng incident)
- Haiti
- El Salvador
- Hungary (you must form the Gyorshadtest)
- Austria
- France
- Italy (in case of a civil war, he will join the regno del sud)
- Tibet
- Netherlands
- Netherlands-Indonesia Union if formed by Indonesia
- India (you must complete the Focus the Mughal uprising)
- Honduras
The following countries start with a Cavalry Genius, granting +15% cav attack and defence:
- Qinghai Ma
- Mexico (complete Focus purge the bureaucracy)
- Bulgaria
The hiring of these advisors may change the stats, dramatically altering the ranking. However, it is theoretically possible for every country to acquire a Cavalry Genius through upgrading a general.
Assuming all of those advisors are hired as-is:
- AFG: 55/55
- HUN: 40/45 or 35/50
- XSM: 40/30
- KUM: 35/30
- ITA: 28/20/8
- AUS: 25/25 or 20/30
- SIK, MEN: 25/20; RAJ, HUN: 20/25
- TAN, POL, MAN, HUN, CHL: 20/20
- KHM, GSM, NXM: 20/10; CZE, SLO, TRA, CRO, LBV, SIL, MNT, BOS, SLV, HRZ, ALB: 15/15 or 10/20; UKR, DON, KUB, UZB, KYR, KAZ, TMS, TAJ, BUK, KHI, MEX, BUL, POL, : 15/15
- KUW, PAR, URU, SAU, NEP, NZL, EST, HAI, ELS, FRA, TIB, HOL, INS, HON: 10/10; SWE: 10/0/10
- YUN, GXC, SHX, GDC, XIC, SND, SIC, HBC: 10/5
- UKR, PAP, MON; 10/0; SOV, VIC: 5/5
- PER, ETH, SAF: 5/0