Chapter 1 lays out the central theoretical arguments of the book. It argues that three factors played a key role in the emergence of democracy in region: the professionalization of the military, the rise of strong opposition parties, and splits within the ruling party. It analyzes what led to the professionalization of the military and the rise of strong opposition parties and it shows how they led to varying regime outcomes in different South American countries. This chapter also discusses why existing theories of democratization cannot fully explain the emergence of democracy in the region

Chapter 8 examines the failed struggle for democracy in Bolivia, Ecuador, and Paraguay during the late nineteenth and early twentieth century. In contrast to the other South American countries, Bolivia, Ecuador, and Paraguay made relatively little progress in professionalizing their armies in the early twentieth century and were not able to establish a monopoly on violence. As a result, the opposition, especially in Paraguay and Ecuador, continued to seek power via armed revolt, which undermined constitutional rule and encouraged state repression. The weakness of parties in Bolivia and Ecuador also enabled presidents to manipulate elections, resist democratic reforms, and run roughshod over the opposition.

Chapter 6 examines how parties and the military shaped democracy in Argentina and Colombia. Both countries were ruled by authoritarian regimes in the nineteenth century that manipulated elections to remain in power. A strong opposition party, the Radical Civic Union, arose in Argentina in the 1890s and this party initially sought power through armed revolts as well as elections, but the professionalization of the military at the end of the nineteenth century made armed struggle futile. The Radicals pushed for democratic reforms but could not achieve them until a split within the ruling party led dissidents to come to power. After passage of the reforms in 1912, the Radicals won the presidency, but Argentina then lacked a strong opposition party, which undermined democracy in the long run. In Colombia, two strong parties arose during the nineteenth century and whichever party was in the opposition sought power at times via armed revolt. Colombia professionalized its armed forces in the early twentieth century, however, which forced the opposition to abandon the armed struggle. The opposition began to focus on the electoral path to power, but was only able to enact democratic reforms thanks to a split within the ruling party. In the wake of these reforms, Colombian elections became relatively free and fair, but the country's military was not strong enough to contain increasing regional violence, which undermined the country's democracy.

Chapter 7 explores the reasons why Brazil, Peru, and Venezuela experienced relatively stable authoritarianism during the early twentieth century. All three countries professionalized their militaries during this period, which helped bring an end to the frequent revolts that had undermined their prospects for democracy in the nineteenth century. None of the three countries developed strong parties, however. The absence of strong parties impeded democratization in several ways. First, party weakness allowed presidents to concentrate authority and extend their hold on power in some cases. Second, and even more importantly, the weakness of opposition parties meant that the opposition had little chance of winning elections or enacting democratic reforms, particularly in the face of widespread government electoral manipulation. As a result, the opposition frequently abstained from elections, which only deepened authoritarian rule in these countries. In some instances, the opposition also encouraged the military to intervene to overthrow the president, which undermined otherwise mostly stable authoritarian regimes.

Chapter 3 argues that the professionalization of the armed forces played a key role in the emergence of democracy in the region by bringing an end to the opposition revolts that had plagued the region in the nineteenth century. It employs an original database on historical revolts in South America to analyze the evolution of political violence in the region. It shows that revolts were frequent in the nineteenth century and undermined the prospects for democracy by overthrowing elected governments and provoking state repression. Most of these revolts came from opposition groups and other forces outside the state apparatus. At the turn of the century, however, most South American countries professionalized their armed forces with the assistance of foreign missions, which led to a dramatic decline in revolts in the region and helped pave the way for democracy. Nevertheless, a few South American countries failed to take sufficient steps to modernize their militaries and, as a result, they remained highly unstable. A series of regression analyses show that increases in military strength and professionalization are correlated with a decline in outsider revolts, but not insider revolts, during this period.

The Conclusion summarizes the main arguments in the book and discusses to what extent the factors that shaped regime outcomes in the early twentieth century mattered post-1929. It also examines the broader theoretical implications of the book, analyzes the extent to which the arguments work in Mexico and Central America, and lays out an agenda for future research on historical democratization.