This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2). This doctoral dissertation in economics examines the diffusion of automobiles and motortrucks on American farms in the early- and mid-20th century ? specifically, the impact of last-mile all-weather road access on said diffusion, and the impact of said diffusion on agricultural productivity. This dissertation also examines the impact of group identity on the decisions of citizens and economic agents as they consider agreements to fully integrate capital, labor, and trade flows between a developed country and a developing country (as has occurred in the European Union). In the U.S., automobiles and motortrucks all but replaced railroads for long-distance travel, both passenger and freight. The pace of diffusion was likely powerfully influenced by access to all-weather roads and farmers were among the early adopters of automobiles and motortrucks. In less developed countries today, there is tremendous growth in the sales of motor vehicles, but lack of last-mile road access slows the diffusion of motor vehicles on farms. Measuring the impact of all-weather road access on uptake of automobiles and motortrucks is critical to reliably modelling the future of climate patterns, world transportation networks, urban growth patterns, demographics, and agriculture. Measuring the impact of automobile and motortruck uptake on agricultural productivity and decomposing the impact into a labor-saving and land-saving component, is critical to better examining in the context of agriculture the induced innovation hypothesis posited by Hicks (1932): "a change in the relative prices of the factors of production is itself a spur to invention, and to invention of a particular kind?directed to economizing the use of a factor which has become relatively expensive." Proposed or existing international agreements liberalizing capital, labor, and trade flows are often politically opposed by many citizens of prospective signatory nations, and sometimes either fail to be adopted or are withdrawn from, despite overwhelming consensus and a high degree of confidence that such deals will result in boosts to the national incomes of all signatory nations (and general efficiency gains to the world economy as a whole). Understanding the impact of group identity on political decisions in favor or against economic integration is critical to understanding events such as the eastward expansion of the European Union, the Brexit withdrawal, and various nativist movements surging throughout the developed world. For the dissertation chapter on the impact of road access on automobile and motortruck uptake on farms, a panel data set of counties is developed from U.S. Agricultural Censuses from 1929 to 1959, the period of most rapid diffusion of motor vehicles on farms. In OLS specifications with road access as a single variable with county and state-by-year effects and multiple controls, road access was associated with usage rates that were 4.6% higher for motortrucks and 2.8% higher for automobiles. IV estimation based on a polynomial spatial-lag instrument indicates that road access caused usage rates to be 3.6% higher for motortrucks and 4.2% higher for automobiles. These averages disguise a great deal of heterogeneity in the effect of road access. The impact of road access differed markedly by the types of crops and farm products produced in a county. When examining the impact of automobiles and motortrucks on agricultural productivity, a CES-translog, a Cobb-Douglas translog (with the interaction terms), and a log-log (without the interaction terms) production function of farm enterprises will be estimated, with each observation being the farm enterprises in a single county. The effect of each factor of production will be allowed to vary based on the crop composition of the county. Demographic, climate, and weather control variables will be controlled for at the county level. Changes in total factor productivity will be examined. The impact of automobiles and motortrucks will separately be decomposed into labor-saving and land-saving components. The experiment examining the impact of group identity on economic integration is motivated by the Metzler-Richards labor supply model as adapted by Agranov and Palfrey (2015) and a voting model that actualizes the Median Voter Theorem. One may hypothesize that taxation rates selected would be higher among populations with stronger in-group sentiment, and that conditional on a given taxation rate stronger in-group sentiment will cause the electorates of countries with higher-skilled workforces to be less likely to vote in favor of integration. However, the ultimate impact of in-group identity on the integration vote of the electorates of countries is theoretically indeterminate, as although conditional on a taxation rate in-group identity may cause fewer votes to be in favor of integration, in-group identity increases the tax rate enacted and the likelihood of a subject in countries with more-skilled workforces voting for integration is increasing in the tax rate. The results of the experiment will show which of these two effects is greater. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.