Anthrax bacteria produce spores that can be processed to become easily airborne.
Mail-sorting machinery can easily aerosolize anthrax in envelopes sent via regular methods through the US Postal Service.
Anthrax spores can be spread in the air by missiles, rockets, artillery, aerial bombs and sprayers.
Anthrax can travel downwind for hundreds of miles.
Anthrax spores remain dangerous for decades.
During WW II the British experimented with anthrax on Gruinard Island. 40 years later, the island was still uninhabitable and had to be decontaminated.
Naturally occurring anthrax spores remain dormant in the soil for decades. Grazing animals can ingest them and become infected with the disease.
Anthrax can be produced in large quantities with relatively basic technology.
All of the technology needed to produce anthrax is considered dual use--meaning it has legitimate uses in the biological and pharmaceutical industries.
The technology is available on the open market with few controls to purchase.
Any country with basic healthcare or a basic pharmaceutical industry has the expertise to produce anthrax.