I am not sure what exactly you are talking but some points for you to understand the history and nature of Japanese letters:
1. Kanji (ideogram) letters were introduced (imported) from China about 1500 years ago. I guess it came in with the introduction of budhism.
2. Katakana and Hiragana (both phonogram) were invented by Japanese about 1300 years ago by deforming Kanji to simplify on order to describe easiliy the original Japanese language. Calligraphy helped this movement.
Hiragana is aledgedly a transformation of Kanji ΐBKatakana A is from the left half of Kanji ’.
3. The names of foreign things including the country names like America had to be written in some way since late 19th century. So they used both Kanji(ideogram) and Katakana (phonogrma) to destribe them in writing. Funny thing was they used Kanji as phonogram because Kanji was the official letters in official documents. They picked up the same sound from tons of Kanji letters.
America = ΔΑ in kanji or AJ in katakana
Germany@=@Ζν or hCc
Holland = ’Ι or I_
Both read the same sounds.
Therefore, most of the nations have their own Kanji notation in Japanese.
Nowadays, katakana is normaly used to write the names of foreign countries in documents. But in some cases like when you want to say 'American minitary' in news paper, it is wrtten like ΔR@(Δ from ΔΑ and Rmilitary) because it is shorter and save space. If you use in this case, it means Asia. So the second letter is picked.
Hope this does not confuse you.