President Trump's use of Twitter is the subject of voracious debate. Short term market volatility has been attributed to Trump's tweets. Learn more here.
Wherever commerce occurs, the exchange takes place in a market. Securities require actual or figurative (in person or digital) markets for transactions. Globally, securities markets give a place for exchange, and can be centralized, such as the NYSE, or decentralized, as in the forex market. Read more about global markets and the indices and exchanges that populate them.