Heart of Europe: A History of the Holy Roman Empire, the magnum opus of Oxford’s Peter H. Wilson, is almost a thousand pages explaining a thousand-year empire that few contemporary readers know or care about. Yet the long-ago, expired heart of Europe still has a vital message for the United States today.

All any Brit or American can recall about this empire, which lasted longer than Rome’s, is perhaps Voltaire’s leitmotif that it was neither holy, Roman, nor an empire. Probably true—but that would be to list its strengths rather than weaknesses, notwithstanding the French cynic’s intention.

It was not holy since it separated church and state better than other powers did at the time. It was not Roman but Germanic (which is why Frenchmen so loved to promote the Voltaire jibe). It was not an empire but a federation, the most successful one before the United States, and for similar reasons. It was based upon compact and decentralization rather than primarily relying on top-down coercion to force uniformity.

Wilson, the academic historian par excellence, saves that wisdom until the very last paragraph of his many thousands. His is a history of such magnitude it is impossible to do it justice in a review. Just consider the range of different dynasties: Carolinians (119 years), Ottonians (105), Salianians (101), Lothar (12), Staufers (116), little kings (93), Luxembourgs (90), and the incredible (and better-known) Habsburgs (368). At best, Anglo-Saxons are familiar with Charlemagne and maybe Charles Martel from the Holy Roman Empire’s beginnings, and with the Habsburgs—although knowledge of them is generally confined to Franz Joseph’s abdication after the First World War, well after the demise of the empire, which expired in 1806 to deny the emperor title to Napoleon.

This book makes the case for continuity for the whole millennium between 800 to 1800 A.D., even though there were sustained periods without an emperor during the above-mentioned dynasties. (Under the Hapsburgs, the interregnum was for only three years.) Wilson’s argument is convincing since it was the inability of the electors to agree upon a replacement emperor, or disputes between them, that caused the vacancies. Both elector and non-elector princes continued operating under the same laws and courts during those interludes.

The scope of the empire’s territory was immense, with the boundaries constantly changing in ways to befuddle moderns who look at the old maps and are unable to fit the duchies and principalities into modern nation-states or regions. Ruling nobles fool us with numerous noncontiguous properties that were the result simply of where they could exercise power or, more often, marry their children. Many units survive but just as many do not, having been effaced by modern place-names. The most local elements do endure, many tracing back to remnants of the “original” Roman Empire (which ended in 476 A.D.), with many still on the castle tours today.

The central structure of the Holy Roman Empire was based upon the only ideal its inhabitants knew: the old Roman Empire from which it devolved. The earlier model was modified substantially by three major countervailing forces: fierce German tribalism, a Christianity with deep roots in much of the population before the fall, and finally, an east-west rather than a north-south trade and communications orientation. The empire’s sinew was a network of vassals who formed links from the very top to the remotest outposts: from the emperor, kings, dukes, princes, and lords down to the lowest knight, with the commoners mostly left to supervision by the lower nobles, the bishops (who might also be secular lords), and the minor clerics and abbots.

The vast hierarchical and interconnected vassal system was a military, family, social, and commercial line of communication between the various parts linking all aspects of empire life. Its vaunted legal system was built around the mutual obligations up and down the hierarchical line. Maintenance of the structure was the main business of the realm, as well as a major cause of disputes, whether charges of disloyalty emanating from above or refusals of support emanating from below. The ultimate power at the top was to unseat vassals, but this was exercised sparingly so as not to threaten the whole system of authority. Charlemagne and his early successors removed dozens rather than hundreds. The ultimate power from below was to switch loyalty from one superior to another.

Governance resided at emperor, prince, and local levels. The emperor had two main functions: to keep the borders safe, especially from various Viking, Slav, Magyar, and Muslim invasions; and, just as important, to travel throughout the realm carrying the flag of office and settling inter-principality disputes with his traveling court, from which lower and disbursed courts emerged. Under the Holy Roman Emperor, the prince pretty much ran his fief as he saw fit as long as the emperor’s interests were respected and he could persuade his vassals. Each lord below operated upon the same principle. Still, by the high Middle Ages, most manor, parish, and village settlements had some degree of self-governance.

The top princes were designated electors who chose the emperor himself and of course ruled their own realms, traveling and dependent upon lower vassals they could likewise remove—but with circumspection because the latter, if they united, could remove him by force or by subterfuge. The local lord supervised the processes of production—mainly agriculture, but later trade and water, and then steam-powered manufacturing. Political power so widely distributed required living with differences and disagreements and negotiating, with war only a last resort where all suffered. Religious beliefs encouraged these same attributes, and Europe in this period enjoyed substantial interludes of “public peace” often binding on the emperor himself, up until the Black Plague of the 14th century, which undermined both religious and civil authority.

The legal structure was a large part of the empire’s success. Law was a mix of Germanic folk custom embedded deep in “barbarian” tribes and cults, old Roman law, and church canon law, all of which evolved over time both from below and from above. Emperors, princes, and principalities could come and go, but the law and courts survived (although also in various evolving forms). Major reforms began as early as the reforming 9th century Cluny Benedictine monastic movement, which refined practices that had to appeal to a ruling class based upon muscle rather than rationality. With the diocese and monastery’s own large property base and overlap of religious and economic functions, it meant that canon law, and the church as a legal venue, gained appeal as compared to the nobles’ trial by ordeal and fire. This rationalizing of law then spread to higher church venues, the principalities, and the empire itself.

While all of the important regions in the empire were derived from tribal names (Bavaria, Franconia, Frisa, Swabia, Saxony, and Thuringia), the dominant Franks represented only 25 percent even in the early Carolingian period. Tribal practices set the foundations of law, language, and customs but these tended to be compromises as different ones interacted with each other and laws from above provided some commonness. Over time, ethnic group, ancestry, marriage, and custom became less important than formal law, although these persisted in local symbols of flags, coats of arms, badges, and colors throughout the life of the empire.

Property rights emerged from local tribal markings and later fences and walls, which set family boundaries and ultimately individual ones. These were recognized in law mainly in resolving disputes in court, mostly based on custom and possession. The rise of commerce in cities and guild associations sparked further written uniformity for wills, agreements, and contracts. As with all Europe, Latin provided a common language for the rulers developed around the church, whose scribes did most of the writing. But German replaced Latin in the 13th century as the official language of the empire, two centuries before English became dominant across the channel, although Latin, Italian and Czech persisted too.

With the church demanding some separation from Caesar and holding large areas of property, disputes were inevitable at all levels. The most dramatic was the so-called Investiture Dispute between emperor and church lasting between 1073 and 1122. Traditionally, the king or emperor would give the church-selected bishop a staff to recognize his shepherding the church flock and the bishop would give the king a ring to acknowledge his secular rule. Henry IV invested the archbishop of Milan without church approval, whereupon Pope Gregory VII declared it invalid, infuriating Henry since the archbishop had secular power, too. It was not settled until the Concordat of Worms in 1122, with the emperor—after three days’ penance standing in the snow—conceding that the church council and pope must invest bishops with spiritual authority but the emperor would supervise the council proceedings and help resolve disputes, with the bishop then pledging loyalty to the emperor, a compromise that lasted until the time of Napoleon, almost 700 years.

Such agreements between emperor, lords, and church setting rights and obligations became common in the high Middle Ages. Concurrent with Magna Carta, Emperor Frederick II issued similar charters recognizing secular and religious rights in 1220 and 1231, and the Aragonese Privileges were adopted in 1283. A perverse result of the agreements that granted rights to many levels of society, but were actually enforced by the higher lords, was that the top princes actually gained power relative to the lower nobles and widened the class distinctions between them. Henry IV’s weakness led to numerous military threats to the throne, including from his son, ending in the Salianian wars and finally the peacekeeping Staufers after 1138, and a return to the more consensual rule that was more typical of the empire (with Prussia the main continuing exception), while the rest of Europe turned toward Divine Right centralization.

By the 15th century, the empire became more identified with a common German language and a more uniform legal system protecting property and liberties. A major Turkish invasion in 1469, however, created disorder among the princes over strategy and obligation to the states under attack. Victory was followed by relative peace, with France busy with internal dynastic and religious struggles. Ethnic nationalism did not develop within the empire until the 18th century. It even survived the Reformation, for it ended up containing Protestant and Catholic principalities. But it changed again in 1699, after the Hapsburgs won large territories from the Ottomans, giving the dynasty larger plots of land outside the empire than within.

The Hapsburg kings’ interests then began to diverge from those of the empire’s princes, especially Prussia, with the princes divided in the War of the Austrian Succession. The Hapsburg monarchy actually outlasted the empire, only petering out at the conclusion of the First World War.

The empire’s rule was long, with great differences over time but it held together with multiple layers and divisions of power accepting disagreement and contracting with other power centers as a means of avoiding constant war or dissolution. In effect, the empire invented federalism. Johannes Althusius is normally identified as the first philosopher of federalist contracting between center and periphery (contrasted to the centralizing thought of his contemporary, Thomas Hobbes); but Althusius formulated his theory based on the already-existing reality that linked his Catholic emperor, Lutheran prince, and Calvinist city. While some question whether the Baron de Montesquieu read Althusius, he followed him, and did use similar arguments that would come to exert a strong influence on the American Founders.

Unfortunately, federalism, which President Reagan called the secret of America’s success, became weakened when President Wilson convinced our intellectuals that centralized, scientific administration was the better theory, and this error has dominated U.S. politics from Wilson’s day to ours. But the Wilsonian myth is showing ever more and ever deeper cracks, with widespread agreement today that the center does not hold. Indiana University Professor Vincent Ostrom made the intellectual case as early as 1974 that bargaining among equals produced superior results than force. Today a politically centrist professor writing for the Brookings Institution concedes that the center does not work, crushed by its layers of bureaucracy and red tape. Donald Trump understood the dissatisfaction and rode it to the White House.

Heart of Europe does not directly consider modern political implications, but the author does criticize the European Union at the end as too centralized and suggests a more decentralized and consensual union that might look back upon the empire for valuable lessons—especially now, in the wake of Britons’ decision to leave the EU and the Italian rejection of a more centralized constituion.

The memory of the decentralized empire inspired the success of Konrad Adenauer’s federalism in Germany after the Second World War, and it might even inspire a new American administration as its looks to reconnect its alienated rural base to the heart of its own dysfunctional empire.