The population reflects the potential of a society or nation, and population structure has consistently garnered attention as a key factor in shaping government policies and administration. Moreover, it has been demonstrated that marriage and childbirth are crucial factors in explaining population increase and are indicators of a society's viability. This dissertation, consisting of three essays, examines how government policies affect people's decisions about having children. This will be accomplished by analyzing the policies of OECD member nations, with a particular emphasis on the cases of South Korea--which has the lowest fertility rate in the world--and the United States--which places a higher priority on immigration and abortion restrictions. The dissertation will present both theoretical and empirical evidence in the field of public administration and policy concerning fertility issues. In the first essay, a noteworthy point is the family policy-related expenditures used by OECD countries, where services such as childcare and education were statistically insignificant and demonstrated the lowest policy impact. On the other hand, financial support and tax breaks favorably influenced fertility. Administratively and in terms of policy, state tax benefits impact people's reproductive choices most, and this strategy can provide the most effectively implemented policy outcomes for enhancing the total fertility rate. Consequently, it follows naturally that greater state engagement in service delivery will not improve fertility results. The OECD Family Database displays that many OECD nations with low fertility tend to prioritize service spending. Therefore, the chapter's findings suggest that tax breaks, which influence people's fertility behaviors, should be prioritized when designing policies to address low fertility. The second essay employed a spatiotemporal model to assess the effects of low birthrate response initiatives with a policy bundle approach to supplement the variety of policy environments. The policy bundle approach identified and measured variables that impact fertility trends from the pertinent legislation of 226 local governments in South Korea. The study examined legislative strengthening, increasing support for first-born children, and financial incentives as policy bundles, examining these laws since the timing of fertility-related legislative revisions has the greatest influence on the birth rate. The chapter results showed that the policy bundle significantly affected all birth order rankings, with a trend for the policy's impacts to diminish with increasing birth order. Thus, to support married couples' ability to conceive and nurture children, policies aimed at families must be strengthened. Given the substantial impact that regional spatial factors have on the crude birth rate, areas where low birth rates are anticipated may need to work together or implement suitable remedies through population impact assessments. Event studies showed that fertility dynamics are influenced by socioeconomic shifts, such as economic crises and rapidly rising real estate values, and that population policies for the lowest fertility rates have been less and less successful in recent years. These changes in the population suggest that the government should adopt more aggressive policy measures. The third essay examines the causality between the abortion restriction and Americans' fertility behavior, concentrating on Kentucky and Illinois. According to the research findings, Kentucky's prospective birthrate is negatively impacted by the abortion restriction. This indicates that while the abortion ban could appear to force childbirth, which would boost births initially, there might be long-term negative externalities. Moreover, the prohibition on abortion may lead to problems with hospital and obstetric services, which might be harmful to maternal and infant health. Thus, this chapter makes the case that the abortion debate ought to be approached from the standpoint of the public interest rather than as a political or religious one. The study suggests that careful consideration of alternatives and thorough policy research should be done before enacting an abortion ban in the United States due to the possible long-term harm to public health. This dissertation offers a theoretical framework and possible empirical models in population policy research. It begins by presenting a model of fertility behavior developed with Ostrom's SES and IAD frameworks. Concerning births, this fertility behavior model shows how the interplay between macro-level national policy and micro-level personal decision-making affects the population. Demographic policies, including state-mandated birth control or abortion ban, have historically impacted individual decision-making, which in turn has affected the demographic structure of the country. This mechanism suggests that population structure is influenced by policy. Furthermore, this dissertation supports Calhoun's experiments by showing that civilizations characterized by fierce rivalry and constrained space may be unable to allocate resources effectively and run the danger of going extinct. A community with just rivalry and no collaboration among its members is unsustainable, and a population confined to a small area suffers. In this sense, the sustainability of humankind depends on increasing human habitat through space exploration or technological breakthroughs.