Short answers, pulled from the story.
The Empire style is an early 19th-century design movement in architecture, furniture, the decorative arts, and the visual arts, representing the second phase of Neoclassicism. It flourished between 1799 and 1815 during the Consulate and the First French Empire, and its influence lasted until the late 1820s.
The Empire style takes its name from the rule of the Emperor Napoleon I during the First French Empire. It was intended to idealize Napoleon's leadership and the French state.
Two French architects, Percier and Fontaine, were together the creators of the French Empire style. Both had studied in Rome and became leading furniture designers in Paris in the 1790s, where they received many commissions from Napoleon and other statesmen.
The Empire style is governed by a rigorous spirit of symmetry and uses Napoleon's emblems, most notably the eagle, the bee, stars, and the initials I for Imperator and N for Napoleon within an imperial laurel crown. It also draws on Greco-Roman motifs such as acanthus leaves, palmettes, lyres, and sphinxes, plus Egyptian Revival motifs like scarabs, obelisks, and pyramids.
The most famous Empire-style structures in France are the Arc de Triomphe of the Place de l'Étoile, the Arc de Triomphe du Carrousel, the Vendôme column, and La Madeleine. All were built in Paris to emulate the edifices of the Roman Empire.
From France the Empire style spread into much of Europe and the United States, influencing the American Federal style and the design of the United States Capitol building. General Bernadotte introduced it to Sweden as the Karl Johan style, and it later evolved elsewhere into the Egyptian Revival, Greek Revival, Biedermeier, Regency, and late-Federal styles.
After Napoleon lost power the Empire style remained in favour for many decades with minor adaptations. Revivals came in the last half of the nineteenth century in France, again at the start of the twentieth century, and again in the 1980s, while it survived longest in Italy partly because of its Imperial Roman associations.