Add 1400-1425 checkpoint: Timur aftermath, Columbus, Northern Ulus, European wars

Major developments:
- Timurid-Indian Empire: massive N. Indian state from Timur's conquests
- Northern Ulus (Novgorod Khanate): expansionist turn, Finland/Baltic conflicts with Kalmar
- Four-way Baltic rivalry: Kalmar vs Northern Ulus vs Germany vs France
- Greater Germany: constitutional crisis (monarchy vs republic), Italian rivalry with Aragon
- Plantagenet France: campaigns against Scotland/Ireland, Burgundy friction
- Zheng He-equivalent: private explorer maps E. Africa, confirms Australia
- Portugal accepts Columbus (~1490s): Indian Ocean blocked by Song/Ilkhanate → Atlantic pivot
- Americas become PORTUGUESE (not Spanish): massive colonial divergence
- Kalmar Union rediscovers Vinland via Norse route (~1400-1420s)
- Song/Ilkhanate early trading posts in India and East Africa
- Americas colonial landscape table: Kalmar (north), Portugal (Caribbean/S.America), France/Castile (later)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

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-## Open Questions (Post-1375 Chronological Development)
-
-1. **Age of Exploration (~1400-1500)**: Who discovers the Americas? Portuguese Atlantic push? Song Pacific expansion?
-2. **Song's North-South crisis**: When does it break open? Second cold wave (~1460)?
-3. **Timur's death (~1405)**: How do successor states fragment? Mughal-equivalent in India?
-4. **Italy**: Renaissance dynamics with changed trade routes? Venice/Genoa as Song goods gateway?
-5. **Reformation**: Hussite reform movement spreading — when does it become a full break?
-6. **Greater Germany**: How is the monarchy vs. republic question resolved?
-7. **Ilkhanate industrialization**: How far does it get by 1836?
-8. **Great Khanate**: Further decline or stabilization after Novgorod + losing Chagatai?
+## 1400-1425 Checkpoint
+
+### Timur's Death and Central Asian Partition (~1405-1430)
+See "Post-Timur Central Asian Partition" table in Trade Routes section for territorial details.
+- Great Khanate recovers Kazakhstan steppe (to Syr Darya) + western Siberia
+- Ilkhanate absorbs Khorasan + western Afghanistan
+- Khoqand Khanate (Timurid remnant) retains Transoxiana
+- Mongol Khanate regains independence (poor, isolated)
+- **Timurid-Indian Empire**: Timur conquered entire northeastern India (Delhi + Gangetic plain + Bengal). After his death, Timurid successor establishes massive North Indian kingdom. Preparing for eventual Indian unification. Faces: Vijayanagara (south), Rajputs (west), Song economic penetration via Burma Road (east), Ilkhanate trading posts on western coast.
+
+### Northern Ulus (Novgorod Khanate): Expansionist Turn
+- Mongol prince, needing revenue after commercial collapse, pivots to **fur trade + territorial expansion**
+- **Northward**: Into Lapland/Kola Peninsula for furs (minimal resistance from Sami peoples)
+- **Westward into Finland/Karelia**: Direct conflict with Kalmar Union (Sweden)
+  - Forest warfare, seasonal raids, fort-building, competing for Finnic/Karelian tribal allegiance
+  - Neither side can deliver decisive blow in taiga terrain
+- **Baltic coast**: Northern Ulus inherits Novgorod's former Baltic proxy territories (Estonia, Latvia)
+  - Now treats them as direct possessions, not Great Khanate proxy management
+  - Cuts into Hanseatic/German commercial space
+- **Baltic Sea returns as a commercial opportunity** — Northern Ulus may partially recover trade income through Baltic fur/timber exports, replacing the lost Silk Road transit role
+- Creates **four-way Baltic rivalry**: Kalmar Union (north/west), Northern Ulus (east), Greater Germany/Hanseatic (south), with Plantagenet France as indirect participant via English North Sea interests
+
+### Greater Germany: Internal Crisis + Italian Rivalry
+- **Constitutional crisis**: Monarchy vs. republic debate intensifies
+  - Likely resolved through compromise: **elected federal leader with limited powers** (Dutch stadtholder-style)
+  - Short internal conflict possible but external pressures prevent prolonged civil war
+- **Italian rivalry with Aragon**: Both powers compete for influence over Italian city-states
+  - Germany pushes from the north (Alps → Milan, Venice)
+  - Aragon pushes from Mediterranean (already holds Sicily, Sardinia → wants Naples)
+  - Italian city-states play both sides (Venice leans German, Naples leans Aragon, Florence/Papacy try to stay independent)
+  - Proxy wars and diplomatic maneuvering, not full-scale conquest
+
+### Plantagenet France: Consolidation + British Isles Campaigns
+- Continental position now stable → turns attention to the islands
+- **Scotland campaign**: Attempts to reconquer de facto independent Scotland. Highland terrain makes it difficult — likely prolonged war of attrition, not quick conquest.
+- **Ireland**: Strengthens coastal garrison control, but full conquest of Gaelic interior unlikely. Pale expands somewhat.
+- **Wales**: Already under control (historical conquest in 13th century).
+- **Burgundy friction**: Ongoing cold war over French legitimacy. Border skirmishes, diplomatic rivalry.
+
+### Ilkhanate and Song: Early Indian Ocean Competition
+- **Ilkhanate**: Trading posts on Indian western coast (Gujarat, Malabar) via Persian Gulf. Economic presence, not territorial conquest.
+- **Song**: Trading posts developing on Indian eastern coast via Burma Road connection to Bengal. Plus maritime network from SE Asian colonies.
+- **East Africa**: Song's Zheng He-equivalent explorer (~1405-1430s) maps East African coast, establishes early contact. Ilkhanate has existing connections via Oman/Yemen → Swahili coast. Both powers beginning to establish presence. **East Africa becomes a future Song-Ilkhanate competition zone.**
+- Neither side confronts the other directly yet — Indian Ocean is big enough for both. But the seeds of maritime rivalry are planted.
+
+### Zheng He-Equivalent Explorer (~1405-1430s)
+- Northwestern Muslim origin (homeland in Hexi/Western Protectorate area, family displaced by frontier expansion)
+- Works in Song's interior, becomes merchant-navigator
+- **Private/semi-official expeditions** (Song's commercial culture, not Ming-style state pageantry)
+- Achievements: detailed mapping of East African coast (Somalia → Mozambique), confirms Australia as continent, possibly reaches Madagascar, opens direct Song → East Africa trade route bypassing Ilkhanate middlemen
+- **Strategic significance**: If this East African route matures, Song can access African gold/ivory without paying Ilkhanate transit fees
+
+### Portugal: Atlantic Pivot and Columbus
+- **1415**: Conquest of Ceuta (Morocco) — proceeds as in history
+- **~1420**: Madeira discovered. **~1427**: Azores discovered.
+- Portuguese explorers sailing down African west coast encounter Swahili/Arab merchants who report that the **Indian Ocean is already dominated by Song and Ilkhanate** → intelligence reaches Lisbon by 1480s
+- **Realization**: The African route to India leads to an already-occupied market, not virgin trading territory
+- **~1484**: Columbus (Genoese navigator) proposes westward voyage to reach Asia. **Portugal accepts** (unlike history where they rejected him)
+  - Historical Portugal rejected Columbus because they believed the African route was better
+  - In this timeline: African route = dead end → western route becomes attractive
+- **~1490s**: Columbus sails west under Portuguese flag → discovers the Caribbean / Americas
+- **The Americas become Portuguese**, not Spanish. Massive divergence from our timeline.
+- Castile (Pedro I's line, more internally focused) is left behind in the Atlantic race.
+
+### Americas: Colonial Landscape Emerging
+| Discoverer | Route | Territory | Timing |
+|---|---|---|---|
+| Kalmar Union | Iceland → Greenland → Vinland (Norse route) | Newfoundland / NE North America | ~1400-1420s (rediscovery of Vinland) |
+| Portugal (Columbus) | Atlantic crossing (Canaries → Caribbean) | Caribbean, Central America, Brazil | ~1490s |
+| Plantagenet France | English Atlantic ports → North Atlantic | Mid-Atlantic North America? | ~1500s |
+| Castile | Late Atlantic entry | Whatever Portugal didn't claim | ~1510s+ |
+| Song | Pacific too wide | Cannot reach Americas | N/A |
+
+### Kalmar Union: Vinland Rediscovery
+- Norway (within Kalmar) retains Iceland + Greenland settlements
+- Norse knowledge of Vinland (Newfoundland) persists in Icelandic sagas
+- Motivations to go further: cod fishing (Grand Banks), timber for treeless Greenland, escaping Kalmar internal politics
+- ~1400-1420s: Norse/Kalmar fishermen and settlers reach Newfoundland, establish seasonal camps
+- Not yet full colonization — fishing stations and timber camps, not conquest
+- Contact with Beothuk/Mi'kmaq peoples
+
+### Bohemia: Reform Movement Continues
+- Hussite-type religious reform spreading across Catholic Europe borders (no nationalist wrapper → ideas travel more freely)
+- Papacy attempts crackdown but reform sentiment reaches Germany, Burgundy, even France
+- No full Reformation yet, but pressure building
+
+---
+
+## Open Questions (Post-1425 Chronological Development)
+
+1. **Song's North-South crisis**: When does it break open? Second cold wave (~1460)?
+2. **Italy**: Renaissance dynamics with German-Aragon proxy rivalry?
+3. **Americas**: Portuguese colonization develops — what do they find? How does it affect Europe?
+4. **Reformation**: When does Hussite-type reform become a full break from Rome?
+5. **Ilkhanate vs Song**: Indian Ocean rivalry escalation?
+6. **Timurid-India**: Unification campaign — when and how far?
+7. **Great Khanate**: Does the Kazakhstan recovery stabilize it or just delay decline?
+8. **Northern Ulus vs Kalmar**: How does the Finnish/Baltic conflict develop?