The Japanese first adapted writing from Chinese; this adapted system is called kanji and is highly similar to, and often homographic with, Chinese hanzi. However, Japanese and Chinese have very different phonological structure: Chinese is mostly comprised of monosyllabic words, whereas Japanese has lots of polysyllabic words. This makes it more difficult to do phonetic transcription in Japanese kanji than in Chinese hanzi.

The Japanese got around this by simplifying the script into a syllabary (every character represents roughly a syllable, or more often, a consonant-vowel pair). They did this twice: one of these syllabaries is hiragana, and the other is katakana. In modern usage, katakana is used largely for phonetic transcription, such as transliteration of foreign words and names, or onomatopoeia, whereas hiragana is used for writing out Japanese words.

As others have pointed out, Japanese has a rather constrained phonological system, so a word like strengths cannot be represented directly but rather more like "su-to-re-n-ge-tsu." Of course, this feature isn't limited to Japanese; it's how an island called "Christmas" gets transliterated to "Kiritimati", just like its parent "Kiribati" is the local pronunciation of "Gilbert." While people think it's annoying, it's largely because they haven't faced languages with challenging transciptions into Latin script. There's a reason why there's a plethora of transcriptions of "مُحمّد‎" after all.