After the July 7th Incident, people across the country united to resist Japan.
Tips
usage
日 here is short for 日本 'Japan'. 抗日 mostly comes before a noun: 抗日战争 'the War of Resistance Against Japan', 抗日英雄 'hero of the war', 抗日根据地 'resistance base area'.
mistakes
抗日 is about resistance in the war. Hostility toward Japan or protests against it today are 反日 'anti-Japanese'.