Herbst (2014) argues that the difficulty African political leaders faced in governing countries divided into multiple ethnic groups, coupled with the dissociation of ownership and control of land, motivated them to develop infrastructure that would extend their authority as far as possible, see also Herbst (2000). The poor or absent state of road networks in most countries in sub-Saharan-Africa leaves a majority of rural people cut off from the centers of political power. Herbst (2000) argues that African governments have been building roads that connect political centers to previously inaccessible areas to expand their power.

Work by Muller-Crepon et al. (2020) relies on a theory according to which the accessibility of ethnic homelands by public authorities is a prerequisite for political leaders to extend their domination over remote areas (Tollefsen and Buhaug, 2015; Raleigh and Hegre, 2009; Buhaug and Rod, 2006; Herbst, 2000; Fearon and Laitin, 2003). Indeed Muller-Crepon et al. (2020) argue that political instability is predominant in areas where political power has very little control over the inhabitants; more specifically, they establish that the ethnic groups’ homelands that are difficult to reach from the national capital are also sites of rebellion and political conflicts. The authors use the map of road networks in African countries to measure access to ethnic homelands from national capitals, and the interconnectivity of ethnic groups. Estimating the effects of these two variables on the occurrence of political conflicts, they show that political conflicts reoccur in areas where there is a weak physical presence of the state. To demonstrate the robustness of this finding, they construct a theoretical network composed of hypothetical road segments that ensure the lowest travel time between the busiest ethnic groups; using these hypothetical networks, they construct instrumental variables estimating what the accessibility of ethnic homelands from political centers as well as the inter-connectivity of ethnic groups would be if these networks existed. .

Their results are robust to the use of these instruments, thus confirming the twofold role of road networks in extending the control of political powers and reducing political instability; political authority and stability are reinforced in ethnic groups that are accessible from the political capital.

We rely on this literature, which highlights the motivation of political leaders to build roads to extend their capacity to govern, to construct our instrumental variable for proximity to the road networks. In so doing, we follow a large literature that shows that non-economic factors play determining roles in the propensity of African governments to invest in the construction of public infrastructure (Bonfatti et al., 2019; Jedwab and Storeygard, 2021; Burgess et al., 2015; Herbst, 2014). In constructing our instrumental variable, we assume that African leaders would built roads to facilitate territorial administration by easing the movement of administration officials and military troops from the capital power center to the rest of the country, and from one location to another (Herbst, 2014; Muller-Crepon et al., 2020). Following these assumptions, we use the map of African ethnolinguistic divisions produced by the American anthropologist George Peter Murdoch in 1959 (Murdock, 1959) to identify the ethnic homelands of each country in our sample. These ethnic homelands are regarded as being exogenous. Using the least-cost path algorithm, we ”construct” hypothetical roads that would link the centroids of different ethnic homelands to each country’s capital city. We proceed under the assumption that the social planner’s goal would be to minimize the construction costs of these roads if they were to be built. We assume that land altitude

> state has pursued provisions of necessary infrastructure such as roads, railways, and airports as means to promote local economic growth and, in turn, integrate ethnic minorities with the Han majority” (p. 33).

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