Hi,
Before answering the question. let us understand what USDA and ISSS are.
The USDA:
The USDA stands for United States Department of Agriculture. It is basically an executive department of federal government of United States that functions in formulation and implementation of laws about food, forestry and farming. The main purpose of the USDA is to make sure that requirements of farmers are met and agricultural industry is promoted.
The ISSS :
The ISSS stands for the International Society for the Systems Sciences.
It basically in an organization running worldwide that aims at promoting  systems sciences. The organization focus on establishment and implementation  of framework based on general system theory. They promote researchers and scientific institutes to communicate and network for international ,national, regional as well as local development.
Similarities between the USDA and ISSS:
Both organizations are spending alot of funding for the research to solve practical problems faced by agricultural or scientific sector.Both organizations support  and provide opportunities for the networking and communication of professionals like researchers to share information on how to practically solve the problems. They are involved in continuous development of science and technology not only in one country but around the globe.
Differences between the USDA and ISSS:
ISSS is basically an organization running worldwide but USDA is a department of United States Federal government entity. However, USDA is working for the promotion of agriculture by providing funding and initiating projects worldwide.The main focus of USDA is the promotion and development of agricultural sector so that sustainable food demand is met by coming years. However, the focus of ISSS is the establishment and implementation of scientific research in diverse fields of science and technology from computer sciences to system engineering.
Hope it helps!
