What is the difference between strategy development and a business case?

business case is a justification for a proposed project or undertaking on the basis of its expected commercial benefit. Is is a short term undertaking and it seeks to support the long terms plans of an organisation which are called business drivers of an organisation. A business strategy development is a long term plan usually providing the entire organisation a road map into the future and sometimes come in as 5-10 year plan and whatever an organisation undertakes should be supporting these strategic objectives

BS serves overall organisation objectives on a long term basis while BC is a sub set of BS and focuses on shorter term impact of  longer term goals. BC helps as a directional guide to see if our BS is on right track

One is to serve a purpose and the other is to resolve an issue

Business strategy is the means by which a business sets out to achieve its desired objectives. It can simply be described as a long-term business plan.Whereas a business case simply addresses the reasoning behind initiating a project or a task. A business case comes in a well written document or sometimes in the form of a verbal argument or presentation. More importantly, the business case, always supports that every resource expended must support specific business need.