Complex sentence: On 22 July 1917, Siam declared war on Germany and Austria-Hungary, twelve German vessels located in Siamese ports were immediately seized, nationals associated with the Central Powers were detained and sent to India.
Split into simpler sentences: On 22 July 1917, Siam declared war on Germany and Austria-Hungary. Twelve German vessels docked in Siamese ports were immediately seized and Central Power nationals were detained and sent to India.