NZ - "Exercise increased caution in the United States due to the threat of terrorism." ..."There is a heightened threat of terrorism in the United States and terrorists remain likely to try to carry out attacks. A number of politically motivated attacks have occurred in recent years, causing multiple deaths and injuries."
Australia - "The United States has more violent crime than Australia, although it rarely involves tourists. Shootings, including mass shootings, can occur in public places"
UK - "Terrorists are very likely to try to carry out attacks in the USA. Attacks could be indiscriminate, including in places visited by foreigners. You should monitor media reports and remain vigilant at all times."
Here's a more general survey of such travel warnings https://edition.cnn.com/2019/08/07/world/us-travel-advisorie...
Also some countries are now issuing travel warnings about the US because of the mass shootings, especially those aimed at visitors.