as a consequence, the DVD players and DVD format are different depending on the TV system in each country.
In countries with the NTSC system, the DVD players usually sold only work with NTSC format DVDs.
In countries with the PAL system, the DVD players usually sold only work with PAL format DVDs.
In countries with the SECAM system, the DVD players usually sold only work with PAL format DVDs. This is because the TV receivers in these countries are able to receive both a SECAM and a PAL signal.