Roman was killed as a result of the battle, which led to the strengthening of Leszek's and Conrad's positions and triggered a war of succession in the Duchy of Galicia-Volhynia.
The early Middle Ages were characterised by a sparse population of these areas, which were settled by both Rus peoples from the east and Poles from the west.
Historical sources do not provide a clear cause, which has led to many different hypotheses based on the analysis of available chronicles and political events from the turn of the 12th and 13th centuries.
[13] A second interpretation is the so-called Greater Poland hypothesis, which indicates that Roman's actions were the result of internal conflicts between the Polish Piasts.
Another factor was the young age and inexperience of Leszek the White and Konrad I of Masovia, which may have weakened their ability to manage the situation effectively.
However, the response of the Polish rulers was decidedly negative - they refused to meet these demands, arguing that Roman, by leaving the battlefield, forfeited his right to any claims.
[6] Długosz further explains that before crossing the Polish frontier, Roman sent emissaries to the Bishop of Volodimer' and asked for his blessing, as he intended to campaign in Poland for three years.
The nature of the expedition, which aimed to intervene militarily in Polish lands, indicates that Roman led a relatively large army, capable of carrying out an offensive deep into the enemy's territory.
[d] Roman, as the ruler of this territory, had the resources to maintain a large and well-equipped army, which gave him a significant advantage in clashes with neighbouring states.
[20] The process may have depended on a number of factors, such as the political situation in the region, the availability of resources, and the time it took to gather troops from different parts of the principality.
Command of the Polish forces was entrusted to the Mazovian Voivode Krystyn, who played a key role in organising the defence and in directing the troops in the decisive battle.
Knowledge of the terrain, effective tactics and probable errors in command on the Roman side played a significant role in the Polish victory.
[21] The course of Roman Mstislavovich's campaign against the Polish lands remains unclear and difficult to fully reconstruct, mainly due to contradictions in historical sources.
According to Długosz, Roman held negotiations with two Polish bishops, indicating attempts to resolve the conflict diplomatically, but these talks were unsuccessful.
The Polish troops were forced to retreat beyond the Vistula, and the Ruthenian army followed their lead, reaching the Zawichost area in the second half of June.
Despite the initial successes, the final fate of the expedition depended on further developments, which required Roman to face logistical difficulties and possible resistance from the Poles.
The Polish troops carefully prepared their positions - the archers occupied the dominant hill from where they could fire, and the cavalry hid behind a bend in the Vistula, waiting for the moment to charge.
The unexpected attack hit Roman's troops with full force, who, surprised and crowded, were unable to organise an effective defence.
The two factions came to an agreement and the Ruthenians released all their prisoners and paid 1,000 silver marks to recover the body of Roman, which was then buried in Volodimer.
Roman's death determined the defeat of the Ruthenian army and ended the Battle of Zawichost, leaving a lasting mark on the politics of the region.
[37] After his triumph, Leszek's reputation took a positive turn, earning him credibility and the trust of Kraków, The Annals of Jan Długosz which would give him temporary power over the city.
[38] Konrad, coming of age, asked for his share of power and at the meditation of their mother and a selected group of aristocrats, the two brothers divide the country under their authority.