Interlingua
There are three other constructed languages in the world that have more than 1000 speakers, Esperanto, Ido, and Toki Pona. Esperanto and Ido were made before Interlingua. Toki Pona was made in 2001. Some people think Esperanto and Ido are easy to learn because they have no exceptions (words that break the rules) but other people think Interlingua is easier because the makers chose all the words to be easy to understand for people who know English, French, Spanish, Portuguese, or Italian, plus languages like Occitan and Romanian, languages that used to be Latin, the language used in Rome a long time ago.