NEMA is most influential only in North America including Mexico while IEC has been adopted in most countries as indicated by its 67 members countries including the US.
Electrical manufacturers are desperate to merge both standards to create a truly global market for a single product. European manufacturers which are mainly IEC have been trying to penetrate the North American market mostly through buy-outs or merger. The same is true with US manufacturers.
Despite the efforts of equipment manufacturers to satisfy both IEC and NEMA standards, the merging of standards in the construction sector may be a nightmare. An example of this is joining an IEC cable to an NEC cable. There are no exact equivalent of cable sizes for either standard. It will either be one or the other.
Another good example for this will be the switchgear. NEMA switchgears are much larger than an equivalent IEC switchgear. Likewise, the voltage ratings and frequencies are different.
For new projects, this may not be a problem but for an expansion of an plant or platform, a good decision which standard to be used is a requirement.