Look at the things you listed -- "technology, economic factors, globalization, outsourcing, aging workforce" -- and ask yourself for each, "how does this create uncertainty for human resource managers?" I'd say that all but the last
do create uncertainty, and that technology, the economy, and ongoing globalization create the most uncertainty. So, your thesis could be that each of these create major challenges for human resources by creating uncertainty. Then you could explain why that is for each of those three things.
Simone, EssayForum.com