[4] Intense extractive activity in the rubber industry, which reached its height in the early 20th century, attracted Brazilians from many regions to the state.

Practically all of the terrain of the state of Acre is part of the low sandstone plateau, or terra firme, morphological unit which dominates most of the Brazilian Amazon.

During the early twentieth century, rubber seedlings were taken to Southeast Asia, where competitive plantations were established, reducing the importance of the Amazon in production.

Acre's decisive contribution to the Allied victory may have helped Brazil attract North American investment to form the National Steel Company (Companhia Siderúrgica Nacional) in the postwar era.

On April 4, 2008, Acre won a judicial debate with the state of Amazonas in relation to the dispute surrounding the Cunha Gomes Line.

[7][8] The BBC's Unnatural Histories explored studies of this area, concluding that the Amazon rainforest, rather than being a pristine "wilderness", has been shaped by man for at least 11,000 years.

The treaties established the riverbeds of the Mamoré and Guaporé to their maximum western limits on the left bank of the Javari as the border between the Spanish and Portuguese territories.

Some few armed bands of Brazilian explorers exploited the rural and unpopulated region,[15] not knowing and little interested in whether they were "controlled" by Brazil, Peru, or Bolivia.

At that time, João Rodrigues Cametá initiated the conquest of the Purús River;[16] Manuel Urbano da Encarnação, an Indian with extensive knowledge of the region, reached the Acre River, traveling up it as far as the vicinity of the Xapuri;[16] and João da Cunha Correia reached the drainage basin of the upper Tarauacá.

Exploitative activities, the industrial importance of the rubber reserves, and the penetration of Brazilian colonists in the region raised the attention of Bolivia, which solicited a better fixation of boundaries.

[20] The growing impoverishment of that region stimulated migratory waves to the states of Rio de Janeiro, Minas Gerais, and São Paulo.

The great fluvial rivers and their tributary systems were full of small ship fleets transporting colonists, goods, and supply material to the most isolated centers.

The governments of Amazonas and Pará quickly established supply houses, which financed various types of operations, guaranteed credit, and promoted the commercial incentive of the rubber tree groves.

[24] The governor of Amazonas, Ramalho Júnior, informed of the agreement by a functionary of the Bolivian consulate in Belém, Luis Gálvez Rodríguez de Arias, sent military contingents forward to occupy Puerto Alonso.

[24] The Brazilian congress, shocked by the arbitrariness of the act, took measures, canceling commercial accords and navigation between the two countries, and suspending the right of travel to Bolivia.

[24] Finally, Plácido de Castro's forces besieged Puerto Alonso, proclaiming the Independent State of Acre, after the capitulation of Bolivian troops (February 1903).

[24] José Plácido de Castro was proclaimed governor of the new Independent State of Acre,[31] and he had to discuss the question of borders in the diplomatic sphere.

[32] The Baron of Rio Branco, who had just assumed the role of Brazil's Minister of External Relations,[33] immediately opened channels which were meant to have put an end to the question.

The simplest problem, with the Bolivian Syndicate, was resolved by Brazil paying one hundred and ten thousand pounds to renounce the contract (February 1903).

[34] Next, commercial relations were reestablished with Bolivia,[24] while a part of the territory on the upper Purús and Juruá, militarily occupied in March 1903, was declared litigious.

Bolivia finally agreed to cede to Brazil an area of 142,800 km2 (55,100 sq mi), in exchange for two million pounds sterling, paid in two installments.

[24] Peru had also claimed sovereignty over the entire territory of Acre and part of the state of Amazonas, based on historic colonial titles.

[21] The studies to determine the borders proceeded until the end of 1909, when a treaty was signed that completed the political integration of Acre into Brazilian territory.

Exercising a prominent role in national exports until 1913,[36] when rubber was introduced to European and North American markets, Acre enjoyed a period of great prosperity.

[39] During the Estado Novo (New State) political ideas involving the valorization of the interior took hold, with the intention of promoting the articulation of more isolated areas.

Rio Branco Airport serves domestic and international flights (by scheduled carriers and air taxi firms) along with general and military aviation.

Cruzeiro do Sul International Airport is located 18 kilometers away from the city center, which helps access to the Alto Juruá region.

The Arena da Floresta stadium in Rio Branco was one of the 18 candidates to host games in the 2014 FIFA World Cup, which was held in Brazil, but did not make it to the final 12 chosen.

The typical food uses duck, tucupi, cassava flour and pirarucu fish, in addition to the huge variety of Amazonian fruits inherited from the Indigenous peoples.

[52] Some singers, activists and artists from Acre: João Donato, Sansão Campos Pereira, Chico Mendes, Sergio Souto and Tião Natureza.