The last document mentioning the brothers and their uncle Albert II as Saxon fellow dukes dates back to 1295.

John II, the eldest brother, wielded the electoral privilege for the Lauenburg Ascanians, but was rivalled by their cousin Rudolph I of Saxe-Wittenberg.

In 1314, the dispute escalated into the election of two hostile German kings, the Habsburg Frederick III, the Fair, and his Wittelsbach cousin Louis IV, the Bavarian.

Frederick the Fair received four of the seven votes in the same election, with the deposed King-Elector Henry of Bohemia illegitimately assuming electoral power, Archbishop-Elector Henry II of Cologne, Louis's brother Prince-Elector Rudolph I of the Electorate of the Palatinate, and Duke Rudolph I of Saxe-Wittenberg, claiming the Saxon prince-electoral power.

[4] This acquisition included much of the trade route between Hamburg and Lübeck, thus providing a safe passage for freight between the cities.

Armies of both cities opened a second front and conquered Bergedorf, Riepenburg castle and the Esslingen river toll station (today's Zollenspieker Ferry).

In 1659, Duke Julius Henry decreed in his general disposition (guidelines for his government) "to also esteem the woodlands as heart and dwell [of revenues] of the Principality of Lower Saxony.

[11] In 1566, Francis I appointed the Superintendent Franciscus Baringius as the first spiritual leader of the church in the duchy, not including Hadeln.

[12] Francis I conducted a thrifty reign and resigned in favour of his eldest son Magnus II once having exploited all his means in 1571.

Magnus II promised to redeem the pawned ducal demesnes with funds he gained as a Swedish military commander and by his marriage to Princess Sophia of Sweden.

[14] The general church visitation of 1581, prompted by Francis II, showed poor results as to the knowledge, practice and behaviour of many pastors.

[17] It constituted the Lutheran state church of Saxe-Lauenburg, with a general superintendent (as of 1592) and consistory seated in the city of Lauenburg, which merged into that of Schleswig-Holstein in 1877.

[18] The violation of the primogeniture, however, gave grounds for the estates to perceive the upcoming duke Francis II as illegitimate.

This forced him into negotiations, which ended on 16 December 1585 with the constitutional act of the "Eternal Union" (German: Ewige Union) of the representatives of Saxe-Lauenburg's nobility (Ritterschaft, i.e. knighthood) and other subjects (Landschaft), mostly from the cities of Lauenburg upon Elbe and Ratzeburg, then altogether constituted as the estates of the duchy (Ritter-und-Landschaft), led by the Land Marshall, a hereditary office held by the family von Bülow.

The relations between Ritter-und-Landschaft and the duke improved since Francis II redeemed ducal pawns with money he had earned as imperial commander.

[20] During the Thirty Years' War (1618–1648), Augustus always remained neutral, however, billeting and alimenting foreign troops marching through posed a heavy burden onto the ducal subjects.

In 1658, he forbade his vassals to pledge or else alienate fiefs, thus fighting the integration of manor estates in Saxe-Lauenburg into the monetary economies of the neighbouring economically powerful Hanseatic cities of Hamburg and Lübeck.

Their weak position was abused by Duke George William of the neighbouring Brunswick and Lunenburgian Principality of Lüneburg, who invaded Saxe-Lauenburg with his troops,[2] thus inhibiting the ascension of the legal heiress to the throne, Duchess Anna Maria.

There were at least eight monarchies claiming the succession,[2] resulting in a conflict involving further the neighbouring duchies of Mecklenburg-Schwerin and of Danish Holstein, as well as the five Ascanian-ruled Principalities of Anhalt, the Electorate of Saxony, which had succeeded the Saxe-Wittenbergian Ascanians in 1422, Sweden, and Brandenburg.

[25] George III ascended in 1760 and endorsed all the laws, the constitution and the Ritter-und-Landschaft of Saxe-Lauenburg by a writ issued in St. James' Palace on 21 January 1765.

In December, the First French Empire (France's new form of government since 1804) ceded Saxe-Lauenburg, which it no longer held, to the Kingdom of Prussia, which captured it early in 1806.

On 1 January 1811, most of the former duchy (except for the Amt Neuhaus and the Marschvogtei, which remained with Westphalia) was annexed to the First French Empire[2] becoming part of the Bouches-de-l'Elbe department.

On 6 December 1815 Frederick VI of Denmark issued his Asseveration Act (Versicherungsacte) affirming the given laws, the constitution and the Ritter-und-Landschaft of Saxe-Lauenburg.

[2] During the First Schleswig War (1848–1851), the Ritter-und-Landschaft prevented a Prussian conquest by requesting Hanoverian troops as peace-keeping occupational forces on behalf of the German Confederation.

By the Treaty of Vienna (1864), King Christian IX of Denmark abdicated as duke and ceded the duchy to Prussia and Austria.