Starting Provinces and Units are based on information by DD
You can find him here at his Site
Medieval: Total War Description
Early Era:
In the last century Poland has profited from the weakness of its neighbours and its strong relationship with the Empire and the Papacy, even though it is only a little over 100 years since Christianity became the religion of its rulers and the pagan ways were abandoned. Polish Grand Dukes swore fealty to the Empire and even made their country subordinate to the Pope in the recent past. Polish military strength has now brought about a break with the Empire, and the independent Polish kings rule in their own right. The borders of the kingdom of Poland are not, however, set in stone - both opportunity and danger wait on all sides.
There is opportunity all around in the petty principalities and dukedoms that owe allegiance to no strong central kingdom, and in the lands of the lesser kingdoms too. With no central authority, these smaller powers can easily fall before to an aggressive, organised attack, and a cunning Polish king can take advantage of his smaller neighbours' weakness. Even the sanction of Mother Church can be relied upon at times for these actions, as there are still many places where pagans can be found, their souls ripe for salvation through conquest. To the east and northeast the people are fierce, but not so organised as in the west. To the west, the pickings are richer but the risks are greater, especially as this is likely to bring Poland into direct competition with Imperial power in central Germany.
And Imperial power can be a problem, especially any Imperial plans for expansion if the Emperor is checked or chooses not to move south or westwards. A wise Polish ruler will realise that he may not be able to defeat the Empire, but he can certainly make it too expensive in blood and treasure for the Imperial army to advance into Poland or keep what it takes for very long.
High Era:
After a century of expansion profiting from the weakness of its neighbours and its strong relationship with the Empire and the Papacy, Poland remains potentially strong, at least for the moment. The Polish monarchy has managed to hold onto many of its relatively new possessions and Polish military strength has allowed resistance to the demands of the Empire as the power relationship changed.
The borders of the kingdom of Poland are not, however, set in stone: both opportunity and danger wait on all sides. Primogeniture - inheritance by the first-born - is not practiced in Poland, and the division of lands between children in every generation can make it hard to keep a kingdom intact; there is a tendency for the King to be the first among equals compared to the nobility. Even with these problems, the neighbouring petty principalities and dukedoms could fall before an aggressive, organised attack, and a cunning Polish King could take advantage of his smaller neighbours' weaknesses. All around are potentially rich pickings but all have risks, especially any expansionary move that will bring Poland into competition with Imperial power in Germany. The Russian princes to the east are less of a threat, but there are new threats beyond them. The steppe peoples are on the move once again, and a Polish ruler who does not keep an eye on Russian ambitions and the steppes is foolish indeed! Equally foolish is to ignore the intentions of the Holy Roman Emperor should his desire for land lead him to look at Polish territory.
The Catholic Church remains strong in Poland, and a useful tool for its kings to exploit, as there are pagans and Orthodox Christians to the east as rivals and (potential) enemies. The support of Mother Church can be relied upon, as there are still many places within reach of Polish arms where souls are ripe for salvation through conquest.
Late Era:
Poland has survived a century of terrible dangers, none more terrible than the attack of the Mongols in 1241. An army of Polish and Teutonic knights was crushed, and the land was spared only when the Mongols miraculously turned, thanks to the death of their ruler through over-indulgence. Fortunately, these ravening monsters from the steppes have not attacked again. Instead, the Poles have been faced with threats from a different direction, as the Teutonic Knights have continued to push against their borders, into lands that Poles have good cause to see as Polish.
The Catholic Church remains strong in Poland, a useful unifying force for any king to use. Heretics have a habit of arising in Bohemia and nearby lands, and there are Orthodox lands to the south and east, the homes of potential enemies. The support of Mother Church can generally be relied on in any attempts to bring these souls to true salvation via the sword.
Poland's borders have changed many times, as lands have been won and then allowed to slip away. Polish kings have lost few opportunities when taking advantage of their neighbours' weaknesses, even as the Teutonic Order has advanced from the west. Behind the Teutonic Order, of course, lie the ambitions of the Holy Roman Emperor. If these can be countered successfully, a warlike and resolute Polish king can still take advantage of his smaller neighbours' weaknesses. The Russian Princes are not, as yet, equals of Poland's Kings and a move to crush them could be successful, if costly. It is, however, foolish is to ignore the intentions of the Holy Roman Emperor. To the west, the Empire remains a structure rather than a royal state in many respects, and one that may be vulnerable. A wrongly timed attack will, naturally, bring down the full wrath of the Emperor.