Keneshia N. Grant's The Great Migration and the Democratic Party: Black Voters and the Realignment of American Politics in the 20th Century highlights the multifaceted political effects of the Great Migration, which was the migration of over six million African Americans from the rural South to their resettlement in the North during the 20th century. As Grant shows, for African Americans, their migration to the North was prompted by many motivations. But, their desire to become full American citizens by being able to vote influenced their political behavior, their political power in northern cities, their ability to elect Black elected officials at various levels of government, and, as northern politicians progressively realized the electoral power of the growing population of Black migrants, their evolution towards becoming major voters in the Democratic Party's electoral coalition.

The Great Migration and the Democratic Party contributes to the current literatures that analyze the development of political parties, American politics, and African American politics. Grant begins by asking “How did the Great Migration influence American politics in northern cities?” (p. 4) Grant's central argument is that the northward migration enabled Blacks to participate in politics, altering northern politicians' interactions with growing populations of Black voters; significantly, the migration also enabled Blacks to elect an increasing number of Black elected officials across the nation.

By meticulously examining the effect of African American migrant voters upon mayoral elections in Chicago, Detroit, and NY City, Grant adds to the conventional narrative that many Blacks primarily converted from being Republicans to the Democratic Party during the New Deal era. As Grant explains, political scientists generally conceive of political change as occurring either in the electorate or in parties' organizations. Grant focuses on the elite level, political parties and politicians, arguing that these actors tailor their strategies and policy positions to shape their electoral support in order to win elections. Grant argues that Anderson's (Reference Anderson1979) theory of mobilization by the Democratic Party is a very plausible explanation for the realignment of Black voters, especially with regard to the millions of Black migrant voters. Anderson argued that the Democratic Party mobilized many immigrants by increasing their voter turnout for the party during the 1930s, rather than changing (or converting) their partisan preferences for the party. Although Grant acknowledges that many Republicans did convert to the Democratic Party, she concludes: “However, the Great Migration transported millions of Black citizens—who were not able to participate in politics previously—to northern cities and effectively expanded the electorate to include Black people for the first time since Reconstruction. Therefore, what looks like a wholesale defection from the Republican Party by the Black electorate can also be understood as the Democratic Party's mobilization of newly arrived Black migrants.” (p. 17)

In Chapters 1 and 2, Grant argues that the Great Migration changed how Democratic elites interacted with Black communities in northern cities because of many Blacks' migration from the South to the North, the migration's changes upon Black migrants' ability to participate in politics, and the changes in white Democratic politicians' perceptions and strategies regarding Black electoral support. The central evidence supporting Grant's argument is her demonstration of the electoral consequence of Black balance of power (BOP) in mayoral elections from 1915 to 1965 in Chicago, Detroit, and NY City. Notable Black leaders such as T. Thomas Fortune and W. E. B. DuBois argued that BOP was a means for Black voters to influence the parties, their policy positions, and their strategies. Some scholars have challenged the concept and argued that it depends upon several assumptions: (1) for the Black vote to be determinative, the white vote must be relatively divided between the Democratic and Republican Parties; (2) it was possible for the white population to be large and unified on issues, making the Black vote inconsequential due to its relative size; and (3) in reality, Black voters were not politically independent because they were unwilling to vote for Republicans. Grant refines the BOP framework by arguing that the perceptions of politicians and political parties about Black voters guided their interactions with them and their beliefs about them as electoral supporters and powerful coalition partners. Grant's argument rests on the assumption that candidates and parties will be more attentive towards groups whose votes they believe will be the most influential in elections: Grant writes, “whether political elites believed that Black voters were the BOP was most important to their decision making.” (p. 29) Grant tests her argument by estimating a BOP for each of the mayoral elections in the three cities from 1915 to 1965 (50 mayoral elections) from U.S. Census data, finding that the Black BOP ranged from 62% (31 elections) with 100% involvement by the Black Voting Age population (BVAP) to 34% (17 elections) with 50% of the BVAP.

In Chapters 3 through 5, Grant provides detailed analyses of the local political and economic environments of Chicago, Detroit, and NY City. Grant uses the framework of her argument to explain how Democratic politicians altered their policy positions and strategies to attract Black voters. Additionally, she completes her argument by describing the successful elections of Black elected officials at various levels of government across the three cities.

The Great Migration and the Democratic Party rewrites the earlier understanding of the development of the American party system and of African American politics, helping readers to understand the political progress of African Americans during the 20th century: how Blacks developed from being acted upon towards becoming transformative political actors in American politics. Indeed, the subject matter of Grant's book endures and is very relevant for understanding the 2020 Presidential election, as it has been commonly acknowledged that substantial Black turnouts in Detroit, Milwaukee, and Philadelphia caused the states of MI, WI, and PA to change from being pivotal states in President Donald Trump's 2016 victory to becoming consequential states in President Joe Biden's victory.