In this passage, there are two losses of the word again. In verse 19, the 1892 RLDS edition omitted the again, and this shorter reading has continued in the RLDS text. The loss was probably due to the eye skipping from again to the immediately following against. Since the Lamanites have already come to war, the next time would be a second time (thus the word again). Moreover, the same language occurs earlier in verse 11: “that ye will not return again against us to war”. For another example where again was lost from the text when followed by against, see under 3 Nephi 2:18 (in that instance, it was probably the 1837 typesetter who omitted the again).
In Alma 44:20, the 1841 British edition accidentally omitted the again. The following LDS edition (1849) restored the word. This is the second time that Moroni has caused the fighting to stop (the first is described in Alma 43:54–44:1); once more the use of again is appropriate here.
Summary: Maintain the two instances of again in Alma 44:19–20; both are helpful in making the meaning clear.