Trading Cross Currency Pairs

My trading account is in USD, so say I want to go short GBP/JPY. Wouldn’t I have to first go short USD and long GBP? And if so, wouldn’t it be like I was in two trades at once and wouldn’t I be affected by changes in both GBP/USD and GBP/JPY?

When you do any trade you’re effectively borrowing the short currency and converting it to the long one. That means there’s no initial conversion from your account currency when you trade a cross. It’s all on the back end of the trade when that comes into play. Your profits or losses will need to be converted into USD, so in your GBP/JPY example the GBP/USD exchange rate will matter. It will never make the difference between profit and loss, but it will impact the size of it.