National unity is a matter of great concern for many countries around the world today. The study of policy evaluation is an important aspect of the study of national unity. The evaluation of policy implementation effects can help policymakers analyze whether there are problems in the formulation and implementation of the policy, thereby promoting further policy adjustments to better achieve national unity. This article adopts thematic searches and a systematic literature review as research methods. Through the systematic review, it summarizes and analyzes the research on national unity policies across different regions and countries. The article has two objectives: First, to explore the current perspectives in the research on national unity policies, and second, to analyze the state of research regarding the effectiveness of national unity policies. Among the 35 papers analyzed, 7 were on integration policy, 6 were on education policy and 4 were on language policy. To a certain extent, this reflects the perspectives of some countries in Europe, Asia and Africa, including France, Greece, Russia, Turkey, China, Sri Lanka, Nepal, Kenya, South Africa, Nigeria and other countries on the governance of national unity. Research on policy effectiveness is mainly conducted from the perspectives of policy content and policy implementation. However, there is little analysis of successful cases that achieved the desired goals. The main contributions of this article are as follows: first, it summarizes and identifies the characteristics of national solidarity-related policies in different continents and countries. Secondly, the experience of the success and failure of the national unity policy is studied and summarized. In addition, this article also found that there are still gaps in the research on successful experiences and causes.

Delay is the leading challenge in completing Engineering, Procurement, and Construction (EPC) projects. Delay can cause excess costs, which reduces company profits. The relationship between subcontractors and the main contractor is a critical factor that can support the success of an EPC project. The problematic financial condition of the main contractor can cause delay in payments to subcontractors. This research will set a model that combines the system dynamics and earned value method to describe the impact of subcontractor advance payments on project performance. The system dynamics method is used to model and analyze the impact of interactions between variables affecting project performance, while the earned value method is applied to quantitatively evaluate project performance and forecast schedule and cost outcomes. These two methods are used complementarily to achieve a holistic understanding of project dynamics and to optimize decision-making. The designed model selects the optimum scenario for project time and costs. The developed model comprises project performance, costs, cash flow, and performance forecasting sub-models. The novelty in this research is a new model for optimizing project implementation time and costs, adding payment rate variables to subcontractors and subcontractor performance rates. The designed model can provide additional information to assist project managers in making decisions.