Sub-Saharan African states have the lowest rates of executive alternation in the world. Despite more than two decades of elections, opposition candidates have defeated sitting presidents in only a handful of countries. In Multi-ethnic Coalitions in Africa: Business Financing of Opposition Election Campaigns, Leonard Arriola argues that the key to understanding incumbency advantage is an executive's control of financial resources. In many races, a united opposition could have defeated the incumbent, but ethnically divided coalitions fractionalise or fail to materialise (p. 7). While an incumbent's own ethnic constituency is too small to win a national election, he can leverage state resources to generate cross-ethnic endorsements. Arriola argues that the primary obstacle to multi-ethnic opposition coalition formation is the opposition's inability to access financial resources that are free from state control. He then shows how processes of financial liberalisation and deregulation enable opposition members to ‘defect from the incumbent regime without fear of financial reprisals’ (p. 19). Opposition coalition formateurs can use resources from the business sector to pay leaders of ethnic constituencies up front and assure them of later payoffs (p. 20).

Arriola analyses two similar cases with divergent political trajectories: Cameroon and Kenya. Both countries had comparable banking sectors prior to independence, but by 1980 Kenya had almost three times the number of private banks (p. 92). Interviews with party elites reveal that financial liberalisation facilitated opposition coordination in Kenya, while government control over the financial sector stifled business support for opposition candidates, and consequently coalition formation, in Cameroon. Arriola complements his findings with a cross-national test of African elections between 1990 and 2005 to demonstrate the positive influence of financial liberalisation on the formation of multi-ethnic opposition coalitions.

Beautifully written, Arriola's book takes us on a tour of African economic policy highlighting politicians' attempts to manipulate commercial banking and the conditions that have allowed free capital to flourish. In addition to crafting a clear causal story, Arriola introduces rich data on the variation in economic policies and practices in Africa over the last 70 years. He argues that after independence, private banking only emerged in countries where the president's ethnic group was involved in cash crop production for export, since co-ethnics' accumulation of resources posed a lesser threat to executive's political power (p. 68). Later, he shows that structural adjustment was more likely to take place in these countries and that rentier states remained resilient to structural adjustment reforms.

Arriola is precise and rigorous in his analysis. In a thoughtful discussion of political pressure in authoritarian-leaning regimes, he underlines scope conditions that constrain his theory. He provides examples from Ethiopia – where the regime allowed for the growth of private banks but business leaders remain hesitant to openly support the opposition. In doing so, he generates interesting questions about the effect of policy implementation on economic actors' willingness to support the opposition.

Arriola's book is one of the most empirically rich and theoretically important contributions to the study of African politics in the last 20 years. It should be required reading for all students of African politics, comparative political economy and party politics.