Mieszko's son and successor Boleslaw I (r. 992-1025), known as the Brave, builds on his father's achievements and becomes the most successful Polish monarch of the early medieval era.

Boleslaw continues the policy of appeasing the Germans while taking advantage of their political situation to gain territory wherever possible.

Frustrated in his efforts to form an equal partnership with the Holy Roman Empire, Boleslaw gains some non-Polish territory in a series of wars against his imperial overlord in 1003 and 1004.

The Polish conqueror then turns eastward, extending the boundaries of his realm into present-day Ukraine.

Shortly before his death in 1025, Boleslaw wins international recognition as the first king of a fully sovereign Poland.

The building of the Polish state continues during the eleventh century and the first half of the twelfth century under a series of successors to Boleslaw I, but by 1150, the state will be divided among the sons of Boleslaw III, beginning two centuries of fragmentation that will bring Poland to the brink of dissolution.

The most fabled event of the period is the murder in 1079 of Stanislaw, the bishop of Krakow.

A participant in uprisings by the aristocracy against King Boleslaw II, Stanislaw is killed by order of the king.

This incident, which leads to open rebellion and ends the reign of Boleslaw, is a Polish counterpart to the later, more famous assassination of Thomas á Becket on behalf of King Henry II of England.

Although historians still debate the circumstances of the death, after his canonization the martyred St. Stanislaw will enter national lore as a potent symbol of resistance to illegitimate state authority—an allegorical weapon that will prove especially effective against the communist regime in the post-Second World War era.

Sviatopolk I the Accursed and his brother Yaroslav I the Wise struggle for the title of Grand Duke of Kiev.

Sviatopolk's father-in-law, Duke Boleslaw of Poland, intervenes on behalf of Sviatopolk, defeats Yaroslav's armies, and temporarily secures the throne for Sviatopolk.

The expedition is initially successful for Boleslaw and Sviatopolk, who overrun Kiev and send Yaroslav into exile.

It ends with Boleslaw's withdrawal from Kiev and the military defeat of Sviatopolk by Yaroslav, who returns to the Kievan throne from Novgorod.

The return of Yaroslav leads to the golden age of Kiev and the Kievan Rus'.

Chronicles of the expedition include legendary accounts as well as factual history and have been subject to varied interpretations.

Yaroslav has during the past four years waged a complicated and bloody war for Kiev against his half-brother Sviatopolk, who is supported by his father-in-law, Duke Boleslaw I Chrobry of Poland.

During the course of this struggle, several other brothers (Boris, Gleb, and Sviatoslav) have been brutally murdered.

The Primary Chronicle accuses Sviatopolk of planning those murders, while the Saga of Eymund is often interpreted as recounting the story of Boris's assassination by the Varangians in the service of Yaroslav.

Yaroslav had defeated Sviatopolk in their first battle, in 1016, and Sviatopolk had fled to Poland.

Returning with Polish troops furnished by his father-in-law, Sviatopolk had seized Kiev and pushed Yaroslav back into Novgorod.

Boleslaw and his army remain in Rus' for several months, but later leave for Poland.

On his way to Poland, Boleslaw seizes some of the Cherven towns.

Meanwhile, the posadnik Konstantin Dobrynich and other citizens of Novgorod persuade Yaroslav to go to war against Kiev once again.

Sviatopolk is defeated and flees to the steppes.

Soon he returns with the Pecheneg army and attacks Yaroslav on the Alta River, but is once again defeated and flees to Poland, eventually dying on his way there.

Yaroslav now firmly establishes his rule over Kiev.

Yaroslav, in one of first actions as a grand prince, confers numerous freedoms and privileges on the loyal Novgorodians, who had helped him to gain the Kievan throne).

Thus, the foundation of the Novgorodian republic is laid.

For their part, the Novgorodians respect Yaroslav more than they did other Kievan princes; and the princely residence in their city, next to the marketplace (and where the veche often convene) wis named Yaroslavovo Dvorishche ("Yaroslav's Court") after him.

It probably is during this period that Yaroslav promulgated the first code of laws in the East Slavic lands, "Yaroslav's Justice" (now better known as Ruskaia Pravda, "Rus Truth [Law]").