The union definitely shifted Poland's political centre of gravity eastward : it created a common interest in the Russian menace to the long and naturally defenceless eastern frontier, and in the millions of Greek orthodox population in the eastern borderlands. Warsaw was appointed the future meeting-place of the joint diet, thus preparing the transfer of the capital from Cracow to Warsaw. The Union was the last great historical act of the Jagiellonian dynasty: it put the copingstone to the structure of a monarchy which, with growing consolidation, seemed to bear in it the promise of empire.
The origin of the Polish constitution is to be sought in the wiece or councils of the Polish princes, during the partitional period (c. 1279-1370). The privileges conferred upon the mag nates of whom these councils were composed, especially upon the magnates of Little Poland, who brought the Jagiellons to the throne, directed their policy, and grew rich upon their liberality, revolted the less favoured szlachta, or gentry, who, towards the end of the 14th century, combined for mutual defence in their seymiki, or local diets.
The first seym to legislate for all Poland was the Diet of PiotrkOw summoned by John Albert to grant him subsidies; but the mandates of its deputies were limited to 12 months, and its decrees were to have force for only three years. John Albert's second diet (1496), after granting subsidies the burden of which fell entirely on the towns and peasantry, passed a series of statutes benefiting the nobility at the expense of the other classes. These were followed by others of the same kind under his successor Alexander, which, by facilitating import and crippling export trade in the interests of the gentry, enfeebled and degraded the middle class and thereby seriously disturbed the social equilibrium of the State. Nevertheless, so long as the Jagiello dynasty lasted, the political rights of the cities were jealously protected by the Crown against the usurpations of the nobility. The burgesses of Cracow, the most enlightened econo mists in the kingdom, supplied Sigismund I. with his most capable counsellors during the first twenty years of his reign (1506-26).
Sigismund's predecessor Alexander had been compelled to accept the statute nihil novi (1505) which gave the seym and the senate an equal voice with the Crown in all executive matters. Under Sigismund I., some of the royal prerogatives were recovered ; but in his later years the influence of the gentry returned, and the diet succeeded in controlling all the great offices of state. The
Polish parliamentary system, vesting supreme powers in the two houses of the diet, was an established fact. Sigismund II. knew that only a strengthening of the central authority could save the State. But his endeavours to manoeuvre his way between the two rival powers of the magnates and the smaller gentry were, on the whole, unsuccessful. A patriotic party of "gentry democrats" arose, veiling its programme of democratic reforms under the conservative watchword of the "execution of the laws," and deal ing further legislative blows at the trade of the towns and the social status of the middle class. The king, who at first sided with the great nobles against the "executionists," afterwards allied him self with the latter to curtail the power of the magnates by a repeal of former royal grants of land, and by the imposition of a tax on all tenants of Crown lands for the maintenance of the Army (1562-63). Beneficial as this was, it was only obtained at the price of further dependence of the Crown on the szlachta.