Modern republicanism is a contemporary political ideology centered on citizenship in a state organized as a modern republic. During the Age of Enlightenment, anti-monarchism extended beyond the civic humanism of the Renaissance. Classical republicanism, still supported by philosophers such as Rousseau and Montesquieu, was only one of several theories seeking to limit the power of monarchies rather than directly opposing them. Liberalism and socialism departed from classical republicanism and fueled the development of the more modern republicanism.

Republicanism helped inspire movements for independence in former Spanish colonies in the Americas in the early 19th century, and republican ideals and political designs were influential in the new Spanish American republics. Hispanic American republicans drew inspiration from classic and enlightenment traditions, as well as from developments in France and the United States. The role of republicanism in Spanish-speaking Latin America has attracted renewed interest from scholars. During the middle of the 19th century, many Spanish Americans saw their experiments in republicanism as placing the region on the "vanguard" of political developments, according to historian James Sanders.

Many key political figures in the region identified as republicans, including Simón Bolívar, José María Samper, Francisco Bilbao, and Juan Egaña. Several of these figures produced essays, pamphlets, and collections of speeches that drew upon and adapted the broader tradition of republican political thought. Republicanism informed the development of key political institutions in the region, including ideals of citizenship and the creation of civilian militias. Republicanism often enjoyed broad public support. Shared republicanism also shaped the region's diplomatic traditions, especially the focus on regional confederation, international law, sovereign equality, and ideals of an inclusive international society. Diplomats and international jurists in Latin America, such as Andrés Bello, shaped a tradition of "republican internationalism" that connected domestic republican ideals and practices with the region's emerging place in international society.

Brazilian historiography generally identifies republican thought with the movement that was formally organized in the Empire of Brazil during the 1870s to 1880s, but republicanism was already present in the country since the First Reign (1822–1831) and the regency period (1831–1840). During Brazil's early years after its independence, the country saw the emergence of a republican discourse among the writings of figures such as Cipriano Barata, Frei Caneca, and João Soares Lisboa; republican ideology better developed as a political current after the emergence of the radical liberal faction in the crisis of the final years of the First Reign.

During the First Reign, three groups emerged on the country's political scene: the moderate liberals, the radical liberals and the caramurus. The moderates defended political-institutional reforms such as decentralization, without, however, giving up the monarchical system. Their main doctrinal references were Locke, Montesquieu, Guizot and Benjamin Constant. The radicals, in turn, formed a heterogeneous group with almost no representation within the imperial bureaucracy. They were on the left of the political spectrum, along Jacobin lines, and defended broad reforms such as the abolition of the monarchy and the establishment of a republic, federalism, the extinction of the Moderating Power, the end of life tenure in the Senate, the separation between Church and State, relative social equality, the extension of political and civil rights to all free segments of society, including women, the staunch opposition to slavery, displaying a nationalist, xenophobic and anti-Portuguese discourse.

In 1870 a group of radical liberals, convinced of the impossibility of achieving their desired reforms within the Brazilian monarchical system, met and founded the Republican Party. From its founding until 1889, the party operated in an erratic and geographically diverse manner. The republican movement was strongest in the Court and in São Paulo, but other smaller foci also emerged in Minas Gerais, Pará, Pernambuco and Rio Grande do Sul. Only in São Paulo, however, did the movement become a true organized and disciplined party capable of electoral competition. Until Brazil's transition from monarchy to republic at the end of the 19th century, the question of form of government often produced disputes in regional diplomacy and in calls for international conferences.

Dissatisfaction with British rule led to a longer period of agitation in the early 19th century and failed republican revolutions in Canada in the late 1830s and Ireland in 1848. This led to the Treason Felony Act in 1848 which made it illegal to advocate for republicanism. Another "significant incarnation" of republicanism broke out in the late 19th century when Queen Victoria went into mourning and largely disappeared from public view after the death of her husband, Prince Albert. This led to questions about whether or not the institution should continue, with politicians speaking in support of abolition. This ended when Victoria returned to public duties later in the century and regained significant public support. In the early 21st century, increasing dissatisfaction with the House of Windsor, especially after the death of Elizabeth II in 2022, has led to public support for the monarchy reaching historical lows.^{[citation needed]}

In some countries of the British Empire, later the Commonwealth of Nations, republicanism has taken a variety of forms.